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Solid State Physics - Science topic

Theory and applications of solid-state physics.
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The basic scenario where the graph is exponential and we may extrapolate to obtain the bandgap in eV is suggested in research publications on energy bandgap approximation using Tauc Plot. Which peak, however, should I take into account for extrapolation when there are multiple peaks in a Tauc Plot?
The appropriate figure is included.
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Have a nice time and good day!
Please read these papers, you will find what you want:
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In this model, the number of density of available states for the charge carriers near Fermi level comes around 10^22. Will this much number come for bulk insulating ceramics. For the calculation of number of density of available states for the charge carriers near Fermi level, f0 (resonance frequency) is taken as 10^13Hz. Why? Could you please help me.
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I humbly suggest this video.. CBH fitting using Origin 2019 software is included
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Do you consider yourself a real scientist in your field?
As for me, I don't because I don't know the answer of many basic questions in solid-state physics. For instance, from what's the energy origin of orbitalizing electrons? Is is the thermal energy at T>0 or some sort of quantum energy or both? What's exactly the group velocity of orbitalizing electronic waves and its relation to the ground state energy and thermal energy near T=0. I know there exist so many formal definitions of all the above terms! But is the exact relation between them? In particular, the quasi-free electrons in the conduction band (at T>0) what is exactly the nature of their (so-called) velocity in equilibrium, in the inter-collisional paths (between successive scattering with atoms )? Is is just their thermal velocity? or combination of this thermal velocity with some sort of quantum energy?
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Agree on that point, Prof. Waldemar Łasica
Best Regards.
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I am trying to calculate Band structure for the electrode in Siesta. It is a supercell as it should be. Can any one tell me how to unfold the degenerate bands in band structure plot so that I can compare it with transmission?
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Hi,
Is anharmonicity in the phonon will reduce the Tc of that material?
I found in some of A-15 compounds anharmonic effects will be more.  Can these effects will lead to increase in the Tc or Decrease in the Tc?
Thanking you.
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Hello, an answer to this question was provided in these recent papers from our group, which showed that the effect of anharmonicity on superconducting Tc is non-monotonic, at first moderated anharmonicity increases the Tc due to a constructive Stokes/anti-Stokes interference of terms in the gap equation, then reaches a maximum and the decreases owing to too short lifetime of the phonons:
I hope this is of help and happy to answer further questions.
Regards
Alessio
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Dear RG community members, in this thread, I will discuss the similitudes and differences between two marvelous superconductors:
One is the liquid isotope Helium three (3He) which has a superconducting transition temperature of Tc ~ 2.4 mK, very close to the absolute zero, it has several phases that can be described in a pressure - P vs temperature T phase diagram.
3He was discovered by professors Lee, Oshero, and Richardson and it was an initial point of remarkable investigations in unconventional superconductors which has other symmetries broken in addition to the global phase symmetry.
The other is the crystal strontium ruthenate (Sr2RuO4) which is a metallic solid alloy with a superconducting transition temperature of Tc ~ 1.5 K and where nonmagnetic impurities play a crucial role in the building up of a phase diagram from my particular point of view.
Sr2RuO4 was discovered by Prof. Maeno and collaborators in 1994.
The rest of the discussion will be part of this thread.
Best Regards to All.
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Soon there will be a preprint on this subject from our group.
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What are the books/articles to study the crystal structure of nanoferromagnetic materials?
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Dear S
You didn't specify any magnetic materials compounds. Find the crystal structure of nanoscale ferromagnetic materials using JCPDS CARD.
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I am looking for research articles, which describe the synthesis process of Mn3O4 thinfilm on a substrate by a spin coating method.
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Dear Vidit Pandey thanks for posting this very interesting technical question on RG. In addition to the relevant literature references which have already been suggested please also have a look at the following useful article:
Structural analysis of the hausmannite thin film (Mn3O4) by spin coating method
The good thing about this paper is that it has been posted by the authors as public full text on RG. Thus you can freely download it as pdf file.
Good luck with your work and please stay safe and healthy!
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Material Characterization, Solid State Physics, Surface Science, Spectroscopy, Diffraction
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Spectroscopy refers to separating and detecting different wave lengths, by whatever method. For example a simple prism is one method.
Diffraction grating is simply one method of doing this, but diffraction also servs other purposes. ie. atomic arrangements inside materials as in Bragg diffraction.
It is simply multiple interference.
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when a 2DEG is subjected to the magnetic field, the energy is split in the form of Landau levels. and the QHE is explained on that basis. however, in the case of quantized resistance is obtained without a magnetic field. then how Landau levels are formed in QSHE?
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Dear Shlu,
As shown in 4he attached figure , the charge current flows from left to right through a conductor Hall bar. If the charge current is non-polarized (with equal numbers of spin-up and spin-down electrons), the spin imbalance does not induce a charge imbalance or transverse voltage at the Hall cross. If electrons, which are polarized in the direction of magnetization M, are injected from a ferromagnetic electrode while a circuit drives a charge current (I) to the left, a spin imbalance is created. This produces a spin current (IS) without a charge current to the right of the electrode. Spin–orbit interactions again separate spin-up and spin-down electrons, but now the excess of one spin type leads to a transverse charge imbalance and creates a spin Hall voltage, VSH. As the distance, L, between the electrode and the Hall cross increases, the voltage signal decreases, allowing the decay length of spin currents (spin diffusion length lsf) to be measured. More details about SQHE will be presented in Chapter 9 of my Book, about spin transport in nanostructures.
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In non-local measurements, we apply current between two leads and measure voltage on different leads away from the current leads. to calculate resistance, do we need to divide the non-local voltage by current - as such current is not flowing through the voltage leads?
can you please suggest good literature on non-local measurements?
Thanks
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Dear Shalu Pathak, in addition to all the interesting answers,
To understand the role of nonlocality between the current ja(z) and the electrical field applied Eb(z´) to a normal metal, i.e.,
ja(z) = (integral from 0 to infinite) K(z,z')ab Eb(z´)
where the radius of the kernel K(z,z')ab ~ l (the mean free path) please review section 3 of the classical work:
Best Regards.
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I have several confusions about the Hall and quantum Hall effect:
1. does Hall/QHE depend on the length and width of the sample?
2. Why integer quantum Hall effect is called one electron phenomenon? there are many electrons occupying in single landau level then why a single electron?
3. Can SDH oscillation be seen in 3D materials?
4. suppose if there is one edge channel and the corresponding resistance is h/e^2 then why different values such as h/3e^2, h/4e^2, h/5e^2 are measured across contacts? how contact leads change the exact quantization value and how it can be calculated depending on a number of leads?
5. how can we differentiate that observed edge conductance does not have any bulk contribution?
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You distinguish a normal classical Hall efect from a Quantum Hall effect.
Normal size devices exhibit the first, contain considerable number of electrons.
The magetic field acting on the current pushes electrons to one side of the device
and is counteracted by the Hall voltage set up from charge accumulation. Proportionality between magnetic field and Hall voltage for steady current.
Quantum devices contain fewer electrons in narrow or small devices (Nanostructures) . The magnetic field provokes the equivalent of Landau levels that contain the states for electrons. These pass at regular intervals as the magnetic field increases. Thus there are regular jumps
in the electron conductance as magnetic induction increases.(In single electron conductance, or normal quantum hall effect
The fractional quantum Hall effect is believed to be the consequence of electron interactions and quasi particle formation. This is an extremly complicated phenomena, and not nearly as well understood as many would have you believe.
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When a material is in a Topological state, the conduction in 2D TI is due to the edge channel. If I am using a Hall bar structure where I am doing Non-local measurements as can be seen from the attached file. Many papers say that there is edge conductance of h/e^2 corresponding to one edge channel. If in a Hall bar there are 6 terminals. this is distributed as 1:5 and each channel show h/6e^2 resistance. I do not understand why there is only h/6e^2 resistance even though voltage measurement is done at one terminal? please help
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I will second Hadi Jabbar Alagealy here, that paper is all.
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What are the quantum materials? Quantum phenomenon takes place in every material at atomic level. then how to define quantum materials? is Iron (magnetic materials) quantum material as it shows magnetism which is the quantum phenomenon? if not then what are quantum materials?
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Quantum materials are I believe are those materials that exhibit wave behavior, or equivalently particle-wave duality.
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Has anyone encounter Bratu equation (1D second order differential equation) in electronics, solid state physics or optics problems? So far I am aware that Bratu equation is found in chemical combustion problem.
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You can read some information here DOI:10/18500/0869-6632-2016-24-2-77-114
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Generally, we always try to give low input to operate a device. What are the minimum values of voltage for CMOS technology and magnetic field for spintronics technology?
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Please tell me more
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Dear and Distinguished Fellows from the solid-state physics RG community.
Does have anyone read after 20 years the preprint from Prof. Laughlin A Critique of two metals?
I read it when I was a PhD student. I think his opinion after 20 years deserves more attention. Please, feel free to follow down the link to the arXiv preprint if somebody has an interest and please leave your opinion:
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Theoretical calculation of electrons in spin down states of half and full heusler alloys.
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please Saravanan L can you tell me the value of DOS in metal ?
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Just curious to make a list of recommended books/study materials explaining Magnetism in condensed matter physics preferably with emphasis on Quantum Magnetism.
I would be glad if you give some references from Bachelors to Ph.D. level.
Thanks & Regards,
KP
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Dear Kaushick Parui , In addition to all those mentioned, the chapter VII of the book:
Statistical Physics, part II: Theory of the Condensed State, Vol. 9 by E. Lifshitz, L. Pitaevskii Elsevier, 2013.
for the Ph.D. Level - Theory. Mainly talks about magnons.
Best Regards.
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Does electron mobility only depend on the presence of an electron in the conduction band, or low band gap? Please explain.
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Because this question is a basic question I would like to give an answer for it.
In solids when one applies on it an electric field the free charges in it either electrons of holes drift with a steady sate velocity which is proportional to the electric field such that vd=mu E.
The mobility itself mu= q Tau/m*
where q is the electronic charge, Tau is the relaxation time and m* is the effective mass. As said before of one wants to increase mu one has to increase Tau and decreases the effective mass.
The effective mass is a material property because it is related to the second derivative of the energy with momentum of the energy band structure at the minimum of the conduction band and maximum of the valence band.
But the quantity which can be controlled to some extent is the relaxation time Tau.
There are two main scattering mechanisms, the thermal vibration of the lattice and the other is the impurity and crystallographic defects.
One can the thermal vibration by decreasing the temperature.
And one can reduce also the impurities and crystallographic defects.
It remains one point In mosfet transistors the electrons move in a surface channel and they get scattered at the surface defects. In order to avoid such surface scattering one builds a potential well under the surface in which the electrons can move without scattering at the surface because they are not allowed to exist at the surface.
For more information about the mobility please follow the link:
Best wishes
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In the (electro-) conducting materials, as I know, there is an energy gap between the valence band (VB) and the conduction band (CB) that can be brought to or near-to the Fermi level by doping (p-type or n-type dopant).
But ( My question is ), If I want to design a (semi- or super-) conductor's materials (inorganic or polymeric) , Which properties would I look for? and, also, Which characterizations would I consider for the properties' investigations? What are the requirements for the materials' property (with regard to its band structure) to achieve the considered structure-property relationships (or requirements ) for the preparation of the conducting materials?
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Indeed Dear Ahmed MS Dawelbeit it is a very interesting and subtle question, refer to it as a localization phenomenon is one way since electrons can be seen as wave packets that can be or not well defined within the structure (metal, either metallic polimer).
In general, we have a kinetic criterium with three well-defined regions, the product "l . kF", since we understand localization as the absence of diffusion of any kind of waves in a disordered medium.
Please check for the case of metallic polymers, the following reference:
Alan J. Heeger, 2003, The Critical Regime of the Metal-Insulator Transition in Conducting Polymers: Experimental Studies. Condensation and Coherence in Condensed Matter, pp. 30-35
it is very instructive
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Dear RG community, this review thread is about the role of RKKY interaction in solid-state physics. I want to learn more about it. I would like to know for example, what physics effects RKKY describe well.
The RKKY exchange interaction (Ruderman - Kittel - Kasuya - Yosida) is defined as an indirect exchange interaction between magnetic ions, carried out through itinerant conduction electrons.
In rare-earth metals, whose magnetic electrons in the 4f shell are shielded by the 5s and 5p electrons, the direct exchange is rather weak and insignificant and indirect exchange via the conduction/itinerant electrons gives rise to magnetic order in these materials.
Some initial clarifications:
  1. For this thread, the are two types of electrons: itinerant or conduction electrons and localized electrons.
  2. Indirect exchange is the coupling between the localized magnetic moments of magnetic metals via the conduction electrons, while direct exchange occurs between moments, which are close enough to have sufficient overlap of their wavefunctions.
RKKY interaction takes place in metals and semiconductors, where itinerant electrons mediate the exchange interaction of ions with localized oppositely directed spins, partially filled d and f shells.
The physical mechanism is the following: Conduction/itinerant electrons interact with the effective magnetic field of the i-th site of the crystal lattice and acquire a kind of spin polarization. When passing through the next lattice site, relaxation of the magnetic moments of the electron and the site will cause mutual changes in both the spin polarization and the spin of the lattice site.
Hereby, RKKY can be described using the concept that conduction electrons move in an effective field created by a localized magnetic moment of one site.
[1] M.A. Ruderman and C. Kittel, Phys. Rev. 96, 99 (1954).
[2] T. Kasuya, Prog. Theor. Phys. 16, 45 (1956).
[3] K. Yosida, Phys. Rev. 106, 893 (1957).
[4] D. I. Golosov and M. I. Kaganov, J. Phys.: Condens. Matter 5, 1481-1492 (1993).
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The following paper is worth mentioning in this thread:
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Spin orbit torque (SOT) switching of ferromagnetic layer with perpendicular (Out-of-plane) magnetization requires an additional in-plane magnetic field along the direction of applied charge current.
Could any one please give a lucid explanation for the need of such in-plane magnetic field and also please explain symmetry of which is broken by this applied field?
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Magnetization switching by current-induced spin-orbit torques (SOTs) is of great interest due to its potential applications for ultralow-power memory and logic devices. In order to be of technological interest, SOT effects need to switch ferromagnets with a perpendicular (out-of-plane) magnetization. Currently, however, this typically requires the presence of an in-plane external magnetic field, which is a major obstacle for practical applications. Here we report for the first time on SOT-induced switching of out-of-plane magnetized Ta/Co20Fe60B20/TaOx structures without the need for any external magnetic fields, driven by in-plane currents. This is achieved by introducing a lateral structural asymmetry into our devices during fabrication. The results show that a new field-like SOT is induced by in-plane currents in such asymmetric structures. The direction of the current-induced effective field corresponding to this new field-like SOT is out-of-plane, which facilitates switching of perpendicular magnets. This work thus provides a pathway towards bias-field-free SOT devices.
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What is the Exciton's Bohrs Radius? of :
- Boron Nitride (BN)
- Graphite
Anyone know ?,
Or have seen one of these in a paper ?
I'll appreciate it !
Regards !:)
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for the exciton Bohr radius ofhexagonal boron nitride
please see the abstract of:
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The term Condensed Matter is a synonym of Solid-state Physics. Recently, many scientists and researchers replaced their field of specialty and use the term Condensed matter, with its two branches (Soft and hard Condensed matter Physics) to identify weakly-coupled and strongly coupled materials. However, condensed mater includes solids and liquids. If you are interested in these topics, which term you prefer (e.g., to talk about superconductors) and why?
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Solid-state Physics, go back to the old terminology, Prof. Muhammad Hamza El-Saba
I elaborate, nowadays we see many papers with titles such as "nematic supercoductors", but as far as I can recall, a solid-state crystal (solid-state) is not a nematic liquid crystal (condensed matter liquid phase, not just fluid one).
The phenomenological physics based on "free Helmholtz & Gibbs energies" for liquid crystals is something really very "very" hard to calculate and to study, and that is only the classical part of the subject. I cannot imagine how is to deal with by adding quantum correlated many-body phenomena to systems such as liquid crystals.
I can advise reading chapter VI on "the mechanics of liquid crystals" from the book: Theory of Elasticity by Lifhsitz Kosevich & Pitaelskii, 1986, Elsevier, which was previously the Landau Lifshitz VII volume, to understand what I mean.
Best Regards.
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Hello all
I am currently working on lead halide perovskites that are bromine-based. The issue with my material is that it falls out of phase very quickly under ambient settings, and I am trying on ways to keep it more stable, such that its PL also does not degrade. Any suggestions on how I can solve this problem?
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Dear Jitesh Pandya many thanks for your very interesting technical question. te synthesis and processing of lead-perovskites is an important current research topic worldwide. Thus there is a large body of scientific literature available worldwide. From the outside it is difficult to solve your specific problem without knowing the detailed reaction conditions (target compound, starting materials, solvent etc.). For an alternative synthesis of methylammonium lead bromide perovskite nanocrystals using ionic liquids please have a look at the following relevant article:
A facile, environmentally friendly synthesis of strong photo-emissive methylammonium lead bromide perovskite nanocrystals enabled by ionic liquids
Unfortunately this paper has not been posted as public full text on RG. However, the Supplementary Information is freely available (see attached pdf file).
Also please have a look at this potentially useful paper:
Blue-luminescent organic lead bromide perovskites: highly dispersible and photostable materials
There are also a number of interesting references describing the crystallization of lead bromide perovskite materials. For example, please go thorough the following Open Access articles:
Synthesis of centimeter-size free-standing perovskite nanosheets from single-crystal lead bromide for optoelectronic devices
and
Optical Characterization of Cesium Lead Bromide Perovskites
Moreover, I strongly suggest that you use the "Search" function of RG to find and access relevant articles in this field. As an example, you could search e.g. for the term "lead bromide perovskite" and then click on "Publications":
This will provide you with a long list of useful articles.
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Hi There,
I am doing a simulation in COMSOL to find the carrier concentrations in an abrupt p-n junction. The donor and acceptor concentrations are (Nd=3*10^26, Na=10^24) respectively. Unfortunately, there is a mismatch between theoretical and simulated results.
Please read the attached document carefully to understand my question.
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Hello Rana Dey ,
I know that mine will be a rather late answer, but I think I'd better write my opinion.
I think your n-type doping creates a "degenerate semiconductor". If your semiconductor is silicon, if the doping concentration is above 1024 m-3, doped silicon is usually regarded as degenerate, for which the expressions you use (e.g. p=ni2/ND in the n-type region) will start to fail representing the behavior.
Atomic density of silicon is 5x1028 atoms/m3 and the doping concentration should remain much smaller than this, however your n-type doping is not sufficiently small (ND=3x1026 m-3, which means per 100 silicon atoms you have roughly 1 donor atom, which means the semiconductor is degenerate. However, for your p-type doping, NA=1024 m-3, you are at the "official" limits for silicon, so it can be assumed not degenerate yet, for which the expressions can still be valid).
Best regards...
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Generally, when we calculate the carrier density in 2DEG from SdH oscillations (Field dependence of sheet resistance) and QHE (field dependence of Hall resistance) it should match. In some cases it was found that carrier density calculated using both data differ. What is the reason behind this difference? What is the physics behind the calculation of carrier density from SdH oscillations and Hall resistance data?
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It is because SdH oscillation can only occur for those carriers with sufficiently high mobility, whereas in a Hall measurement all carriers are taken into account. So, in cases where transport happens through multi carriers with both high and low mobilities, you may notice such a difference in the value of carrier density obtained from these two measurements.
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i have taken structural mechanics
solid state physic
my design is rectangle shape cantilever.one end fixed and another end will be free.
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Dear Vasu Babu, You can easily plot the frequency with the number of mode and displacement plot by taking a line plot or point plot group. You can also find lots of tutorials in the COMSOL blog.
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Dear RG community, the unitary limit in the amplitude of dispersion * in QM is very complicated and elusive to explain, although there are firmly pieces of evidence, that unconventional superconductors such as HTCSs and Heavy Fermions are mostly in the strong scattering unitary limit at very low energies (temperatures) and a certain range of dopping by non-magnetic impurities. There are also pieces of evidence that point to the same conclusion in Fermi & Bose atomic gases ~,#.
We will publish a preprint on this topic.
I will showcase 3 references in this thread, for now:
* 1. Quantum Mechanics (non-relativistic theory) Landau & Lifshitz, Chapter XVII on elastic collisions, Pergamon, 1977.
+ 2. Superfluid Fermi liquid in a unitary regime by L. P. Pitaevskii, arXiv & Physics - Uspekhi v. 51 p. 603 (2008).
# 3. Momentum-resolved spectroscopy of a Fermi liquid E. Doggen & J. Kinnunen Scientific Reports volume 5, Article number: 9539 (2015)
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Thank you so much for pointing out in this thread the classical textbook by Prof. S. Flugge on practical quantum mechanics, which has served well many generations of physicists.
The book definitely, treats extensively and pedagogically the elastic scattering problem in non-relativistic QM, and also there are a couple of problems dedicated to the phase shift problem and bound states.
Best Regards.
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Valleytronics can be realized by accessing different spins coupled with different valleys. In monolayer TMDs, time-reversal symmetry should be present while spatial symmetry should be broken to realize spin-valley polarization. People use a magnetic field to detect this spin-valley polarization. then why TRS is not broken on applying magnetic field?
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Please look at the introduction of the following paper for the difference between TRS and inversion symmetry first :
In valleytronics, there are several open discussion on TRS, you can check-in:
If one of the two symmetries, in this case, the TRS is preserved, and the inversion not, the states are not protected, as in the case of valleytronics, please check:
Check-in addition to the following external lecture, the part on Kramers degeneracy, one should remember that spin-orbit coupling might or not play a role here:
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Hi all, I am trying to do optical simulation of a simple structure comprising of Si and SiO2 in sdevice. Everything seems to work except for the fact that while visualizing the plots of parameters such as Optical Intensity, I am not seeing any raytracing in the oxide layers. Although light is propagating on to the subsequent silicon layer along the propagation direction, the oxide in between is not populated with the rays in SVisual plot, which is expected. Is there anything I should include in the code to turn on optical raytracing in the oxide ? Any help? Although Sentaurus is taking the right index and extinction values for oxide in the simulation. I checked it.
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Hello Satadal Dutta.I think you made mistake to create geometric model. You have to give coordinates of all layers truly or you must give exactly coordinates and save it for using again in sdevice file. Because this positions is used to create ray tracing in SDevice file.
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Without consulting the phase diagram (of still unexplored alloy systems) , how one can predict which alloying addition in an element would produce intermetallics with some given compositions? For example, how would one say that C is (one of the ) most crucial alloying element of Fe and Si of Al, with just consulting the periodic table and electronic structure? Of course, there is no objective definition of "most useful" alloy- the same alloying element raising strength would not be the one that raises ductility.
Some special properties can be reasoned as
  • Strength and ductility- estimable by formulae for Solid solution, precipitation, dispersion and grain boundary strengthening- but how to physically link solid solution strengthening or Pierres-Nabarro stress of an alloy from electronic structures? Can ductility in these cases also be estimated from first principles?
  • As for thermal and electrical properties, the phonon/electron scattering data may be generalizable for a bigger group of alloys to find out thermal and electrical conductivities- but how? The conductivity drop can be compared between solid solutions and intermetallic formers, but how to be sure that the alloy formed would be of any calculated phase distribution and of this certain electrical conductivity from first principles?
  • Corrosion resistance- The Pilling-Bedworth ratio is related to adherence of oxide or other protective films of metal- but how alloy composition can be related to strength, adherence and composition, and ultimately, reactivity of the protective film? Relative position of EMF series can be, of course, estimated from total lattice energy, ionization energy and hydration energy.
I have just mentioned the two extremes of intermetallic formation and complete immiscibility- (complete miscibilities are well explained by hume-rothery rules, and ultimately also depends on how one objectively measures electronegativity), because there is, to my knowledge, no concrete rules to predict nature of phase diagram (isomorphous or eutectic or peritectic or monotectic or...) between two elements, let alone two compounds.
While electronic band structures of an element are available to be computed by standard methods, there is no systematic way to predict crystal structure or computed thermodynamic properties from composition alone (that are vastly generalizable).
I think there are scientific factors like cosmic and geological abundance, position in EMF series (and hence ease of extraction) as well as socioeconomic factors like market demand as choice for an alloying element. But is it possible to locate useful alloying elements for any of the elements with same unified rationale? (say of Mo, Ru, Rh, Pm, Tl)
And again, is there seemingly any way to tell which pair of metals or elements would be completely immiscible in solid states?
In theory, it is all about minimizing gibbs free energy, and from specific heat data of a solid, one can extract both values of enthalpy and entropy term. If this technique is generalizable for any solid, then why it is not used pervasively? is it because we just cannot predict the specific heat without crystal structure, and from chemistry alone, there is no way to predict crystal structure? Is it not possible to obtain Gibbs free energy of overlapping electron orbitals solely from schrodinger's equation, just like total energy is extracted from eigenvalues of Hamiltonian?
Hume-Rothery rules or Darken-Gurry maps are good starting points, but not good enough. Machine-learning based prediction can make things more systematic but without potentially answering the "why"s in a language familiar to humans . Interatomic potentials are scarce and very rarely generailizable for any group of elements (like Lennard-Jones for gases). My question finally boils down to- prediction of effect of alloying of any two elements, and ultimately composition to crystal structure and phase diagram calculation from first principle- is it even partially possible, if yes, how?
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P.S: Honorable Researchers, Please provide related research papers related to these questions, along with your valuable feedbacks. I am unashamedly open to admit my severe incompleteness of knowledge, and I am far from being master of these field of science. SO feel free to point out where I have mistaken, and also show me approach to synthesize such vast scientific knowledge into a coherent framework.
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See some of my related questions
  1. https://www.researchgate.net/post/What_can_be_theoretical_reason_for_these_patterns_of_Crystal_structures_in_periodic_table?_ec=topicPostOverviewAuthoredQuestions&_sg=qQHz-0jUZMihIai8gwUp1voPk-Tw5-YCl59uQgT88757TE3f6VQz9s6UGLULozUurbHcPQ3VJnXpw-YC
  2. https://www.researchgate.net/post/Is_there_any_special_rule_to_find_out_possible_room-temperature_stable_silicates_chemical_composition_if_not_crystal_structure_itself?_ec=topicPostOverviewAuthoredQuestions&_sg=qQHz-0jUZMihIai8gwUp1voPk-Tw5-YCl59uQgT88757TE3f6VQz9s6UGLULozUurbHcPQ3VJnXpw-YC
  3. https://www.researchgate.net/post/How-etchant-for-a-particular-alloy-system-is-developed-Can-it-be-estimated-from-first-principle-physics-chemistry-and-metallurgy?_ec=topicPostOverviewAuthoredQuestions&_sg=qQHz-0jUZMihIai8gwUp1voPk-Tw5-YCl59uQgT88757TE3f6VQz9s6UGLULozUurbHcPQ3VJnXpw-YC
  4. https://www.researchgate.net/post/What_are_the_factors_molecular_crystalline_structure_related_that_affect_refractive_index_of_ceramics_glasses_and_polymers_How?_ec=topicPostOverviewAuthoredQuestions&_sg=qQHz-0jUZMihIai8gwUp1voPk-Tw5-YCl59uQgT88757TE3f6VQz9s6UGLULozUurbHcPQ3VJnXpw-YC
  5. https://www.researchgate.net/post/How-computational-phase-diagram-techniques-can-find-Gibbs-free-energy-of-a-crystalline-phase?_ec=topicPostOverviewAuthoredQuestions&_sg=qQHz-0jUZMihIai8gwUp1voPk-Tw5-YCl59uQgT88757TE3f6VQz9s6UGLULozUurbHcPQ3VJnXpw-YC
  6. https://www.researchgate.net/post/How_can_symmetry_of_a_crystal_can_be_found_out_from_solely_electronic_structure_of_constituent_atoms?_ec=topicPostOverviewAuthoredQuestions&_sg=qQHz-0jUZMihIai8gwUp1voPk-Tw5-YCl59uQgT88757TE3f6VQz9s6UGLULozUurbHcPQ3VJnXpw-YC
  7. https://www.researchgate.net/post/How_binary_solution_models_were_derived_from_first-principle_thermodynamics?_ec=topicPostOverviewAuthoredQuestions&_sg=qQHz-0jUZMihIai8gwUp1voPk-Tw5-YCl59uQgT88757TE3f6VQz9s6UGLULozUurbHcPQ3VJnXpw-YC
  8. https://www.researchgate.net/post/How_crystal_structure_of_a_one-element_metallic_molecular_crystal_under_a_given_T_P_can_be_estimated?_ec=topicPostOverviewAuthoredQuestions&_sg=qQHz-0jUZMihIai8gwUp1voPk-Tw5-YCl59uQgT88757TE3f6VQz9s6UGLULozUurbHcPQ3VJnXpw-YC
  9. https://www.researchgate.net/post/What-decides-lowest-free-energy-crystal-structure-of-a-solid-at-a-given-temperature-and-pressure?_ec=topicPostOverviewAuthoredQuestions&_sg=qQHz-0jUZMihIai8gwUp1voPk-Tw5-YCl59uQgT88757TE3f6VQz9s6UGLULozUurbHcPQ3VJnXpw-YC
  10. https://www.researchgate.net/post/Why-metal-valency-affects-mutual-solubility?_ec=topicPostOverviewAuthoredQuestions&_sg=qQHz-0jUZMihIai8gwUp1voPk-Tw5-YCl59uQgT88757TE3f6VQz9s6UGLULozUurbHcPQ3VJnXpw-YC
Thank you very very much to hold your patience to read the whole post :)
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You asked a very broad question, but I hope my answer will undercover the understanding of some of the subquestions =)
Due to DFT is a tool, which operates with small atomic systems up to a couple of hundreds of atoms (you can consider and larger cell up to 400-500 atoms, but you lose in CPU time or accuracy of calculations), you can consider either single-phase atomic structures (solid solution or stoichiometric phase) or supercells with an interface between two different phases.
As for mechanical properties, you can estimate them using special equations, which have bulk moduli of considered phase as input parameters.
Bulk moduli can be easily calculated using DFT.
For example, you can read how I recently did that for Mo-Ni-B-C cermet.
From experimental data and mechanical properties measurements, we obtained that precipitation of κ-phase Mo10Ni3C3B decreases a hardness with increasing of stress intensity factor.
Then we calculated elastic constants of precipitated Mo10Ni3C3B and existed Mo2NiB2 and Mo2C phases and estimated bulk properties and hardness using special equations (See Supplementary https://lettersonmaterials.com/Upload/Journals/32862/boev_et_al_supplementary_material.pdf).
The bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio were estimated according to Hooke’s law and the Voigt-Reuss-Hill (VRH) model. For hexagonal polycrystalline crystal:
B=[2(C11+C12)+4C13+C33]/9,
G=(C11+C12+2C33−4C13+12C44+12C66)/30,
E=9BG/(3B+G),
ν=(3B−2G)/2(3B+G),
The Vickers hardness (HV) was calculated according to the empirical formula: HV= 2(K^2 G)0.585−3,
K=G/B
So, we obtained that the new Mo10Ni3C3B phase has a lower hardness and is able to decrease the hardness of the whole material.
Ratio B/G is an indicator for ductility properties.
Bond analysis using electron localization functions (provided in VASP) allowed us to define the nature of the bonding in considered phases.
Covalent bonding means stronger hardness and metallic bonding - more ductility/plasticity.
Also, it is important to analyze the anisotropy factors. That will be able to undercover different useful things.
If you have any questions, do not hesitate to ask me =)
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Hello everyone
Can you please clarify what is difference between field-effect mobility and Hall mobility? which one is more accurate to determine? are both equivalents?
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Carrier Drift and Mobility
Effective Mass and Statistical Considerations
When a free electron is perturbed by an electric field, it will be subject to forces that cause it to accelerate; it moves opposite the direction of the electric field, and would speed up with time. However, the situation in a crystal is different, because the electron is actually moving through a lattice of jiggling atoms that all exert electromagnetic forces. We cannot use the standard electron mass; we must use an effective mass for the electron in the crystal, a result of the periodic forces of the host atoms in the crystal1. The wonderful thing is that in the simple picture, we can view the electron as moving as though it were in a vacuum, but with this new effective mass that varies from material to material.
Another difference is that inside the crystal, a moving electron will not travel far before colliding with a host atom or impurity. These collisions randomize the electron’s motion; therefore, it is useful to use an average time, the relaxation time ττ, which is based on the random thermal motion of the electrons. In fact, the scattering processes of the electron bouncing around causes it to lose energy, which is given off as heat. With the addition of an applied electric field, we also have a mean free path length λλ, or a net displacement on average for a given electron.
Above (Ref. 2): These pictures represent the drift of an electron as a result of thermal motion. In figure (a) where there is no electric field, the electron jumps around but ends up covering no net distance; in figure (b) where an electric field is present, the electron drifts opposite the direction of the field and has a net displacement (and therefore a drift velocity).
This means free charge carriers have a drift velocity, an average speed at which they travel through the material. The average drift velocity for a single electron is the same as the average of all drift velocities of all the electrons, and is given by the following equation:
vd=12aτ=12qτm∗cE(4.1)(4.1)vd=12aτ=12qτmc∗E
where aa is the average acceleration of the carrier, qq is the charge of the carrier (including charge), m∗m∗ is the effective mass of the charge carrier, ττ is the carrier lifetime, and EE is the electric field strength2.
Field Current and Mobility
The movement of charge carriers in an electric field results in an electric current. We will call the current resulting from drifting carriers our field current. The current density J, or the current flow of electrons per unit volume, is given by the following:
Jn=nqvd(4.2)(4.2)Jn=nqvd
Jn=nq12qτm∗E(4.3)(4.3)Jn=nq12qτm∗E
where n is the carrier concentration (per unit volume). Furthermore, we can get rid of the factor of 2 in this equation by averaging the lifetime τ over all carrier velocities1. Therefore, we can now define a quantity called mobility, in this case electron mobility. Carrier mobility is useful as it is the ratio of drift velocity to the electric field strength. Below we will give the mathematical definition and substitute mobility (given as μn) into the current density equation.
μn=νdE=qτm∗(4.4)(4.4)μn=νdE=qτm∗
Jn=nqμnE(4.5)(4.5)Jn=nqμnE
From these equations we can then obtain the conductivity of the material in terms of the mobility2:
Jn=σE(4.6)(4.6)Jn=σE
σ=nqμn(4.7)(4.7)σ=nqμn
The same conditions hold for hole mobility and conductivity, and therefore the total conductivity, which is directly inversely related to the resistivity (the material’s resistance to being conductive, so to speak), is given below:
σ=1ρ=JEqμen+qμhp(4.8)(4.8)σ=1ρ=JEqμen+qμhp
where ρρ is the resistivity, nn and pp are the concentrations of electrons and holes respectively, and μeμe and μhμh are the electron and hole mobilities respectively.
We see that conductivity in a material is directly related to the mobility, which depends on the density of dopants, temperature, and electric field strength. Thus, as mobility decreases conductivity decreases. As materials become more heavily doped, mobility decreases because dopant atoms are very effective scatterers, and therefore decrease the average time between collisions. Similarly, as temperature increases, mobility decreases, however this effect becomes insignificant in heavily doped materials. As electric field increases, the drift velocities of carriers will eventually become comparable to the random thermal velocities. Therefore, high field strength decreases mobility; semiconductors in this way differ from conductors, which so easily generate current that only a low field strength occurs during current flow2. It is worth noting that less specialized impurities and crystal defects in the semiconductor material will also decrease the mobility, because of the scattering effects mentioned above.
References
  1. Green, Martin A. Solar Cells: Operating Principles, Technology, and System Applications. Englewood Cliffs: Prentice-Hall, Inc., 1982. Full book ordering information at www.pv.unsw.edu.au.
  2. Goetzberger, Adolf et.al. Crystalline Silicon Solar Cells. Chichester: John Wiley & Sons Ltd., 1998.
_____
The Hall Effect (and Hall mobility)
_____
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and I claim no originality of creating the image)
The reason of the following structures are given in wikipedia, with some exceptions, at room temperature.
  • usually BCC structure of alkali metal, group 5 (VB) and 6 (VIB) plus Mn and Fe
  • usually FCC structure of Noble Gases (not helium), and near right end of transitional elements?
  • usually HCP structure of group 3 (IIIB), 4 (IVB) and 12 (IIB) and also group 7(VIIB) and 8 (VIIIB, left group) except for first two (Fe, Mn)
  • HCP and DHCP of lantahnides and actinides?
If all of these can be explained in terms of electronic configuration , then a significant electronic-to-crystal structure interrelation in simpler terms can be obtained.
(and possibly, ratio of metallic bandgap or Fermi energy etc. like energy parameters and average electron K.E at room temperature, then I think the correlation would be stronger. Perhaps, if one replaces spherical model of a metallic atom with its feasible 3D dirctional variation of outermost electron shell geometry, the the correlation is likely to be even stronger)
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The trends are well known, but it is difficult to say in a single sentence, why this trends exist. The following can, however, be stated:
-Mn, Fe, Co deviate from the trend because of the magnetic contribution to the thermodynamic functions.
-the total cohesive energy is much larger than the differences between the energies of the crystal structures. So there are non-obvious subtle effects which are responsible for the energy differences and which determine the observed crystal structures. Some quantitative thoughts can be found in
(quick find by google scholar)
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Generally we add spin-orbit interaction as a perturbation term in the system. which system has this spin-orbit term naturally in its hamiltonian.
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There are 2 classes of truly physical effects, which are originated from SO interaction:
Dr. Vadym Zayets classifies them according to the following scheme *:
Enhancement of external magnetic field, localized electrons and atomic gas experience this class of effects. In this type, time-reversed symmetry is broken by the external H.
  • perpendicular magnetic anisotropy.
  • magnetostriction.
  • g-factor.
  • fine structure.
Creation of spin polarization by an electrical current, conduction electrons experience this class of effects, time-reversed symmetry is broken by the electrical current J.
  • spin Hall effect.
  • inverse Spin Hall effect.
  • spin relaxation.
References
Dr. Vadym Zayets, “Spin-Orbit Interaction” https://staff.aist.go.jp/v.zayets/spin3_32_SpinOrbit.html
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A cif file represents a unit cell with minimum energy. My question is, in the start of any ab initio calculation for unit cell generated from the cif file, why we are advised to optimize cell parameters and atomic coordinates both. Can't we just optimize atomic coordinates or perform single point calculation?
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Thank you A.O. Boev and Bojidarka Ivanova for the response. Your answers is very helpful.
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While simulating the effect of a heavy ion strike on a reverse biased SiC Schottky diode in Sentaurus 3D, I see totally different maximum lattice temperatures when simulating different time ranges or even by selection of different number of points to be plotted in the same time range. Everything else including the device structure mesh etc remains the same.
The three solve statements below provide three different temperature profiles -
Solve {
            Poisson
            Coupled(Iterations= 100 LineSearchDamping= 1e-4){ Poisson Electron }
            Coupled(Iterations= 100 LineSearchDamping= 1e-4){ Poisson Electron Hole Temperature}
            NewCurrentPrefix= "Tr_"
            transient( InitialTime=0 Finaltime = 1e-8 increment=1.4
            InitialStep=1e-9 MaxStep=1e-8 MinStep=1e-25){
            coupled{ poisson electron hole Temperature}
            CurrentPlot ( Time= (Range= (0 1.0e-8) Intervals= 200))
    } 
}
Solve {
            Poisson
            Coupled(Iterations= 100 LineSearchDamping= 1e-4){ Poisson Electron }
            Coupled(Iterations= 100 LineSearchDamping= 1e-4){ Poisson Electron Hole Temperature}
            NewCurrentPrefix= "Tr_"
            transient( InitialTime=0 Finaltime = 1e-8 increment=1.4
            InitialStep=1e-9 MaxStep=1e-8 MinStep=1e-25){
            coupled{ poisson electron hole Temperature}
            CurrentPlot ( Time= (Range= (0 1.0e-8) Intervals= 2000))
     } 
}
Solve {
            Poisson
            Coupled(Iterations= 100 LineSearchDamping= 1e-4){ Poisson Electron }
            Coupled(Iterations= 100 LineSearchDamping= 1e-4){ Poisson Electron Hole Temperature}
            NewCurrentPrefix= "Tr_"
            transient( InitialTime=0 Finaltime = 1e-7 increment=1.4
            InitialStep=1e-9 MaxStep=1e-6 MinStep=1e-25)
            {
            coupled{ poisson electron hole Temperature}
            Plot ( Time= ( 1e-13; 5e-13; 1e-12; 5e-12; 6e-12; 1e-11; 1e-10; 1e-9; 1e-8; 1e-7) noOverwrite )
    } 
}
Would anybody have an idea of what could I be doing wrong ?
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I had the same problem. Did you solve this problem?
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Any help to get the book titled Solid State Physics, Solid State Devices And Electronics. By C. M. Kachhava
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Dear Jamal M. Rzaij,
Yes, I will provide you , surely.
Please don't worry, I will send you.
Best Wishes
N Das
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Magnetic mirrors are well known in plasma physics. In order to work, the mean free path of the charge carriers has to be at least as long as the helical paths under the influence of the B field. Therefore, magnetic mirrors exert no mirror effect on the conduction electrons in metals under usual conditions. However, ultra-pure metals at low temperature provide a mean free path of several millimeters. If the mean free path becomes longer than the dimensions of the specimen, the conduction is called ballistic.
If a magnetic mirror had the same effect on a "ballistic electron gas" as on a plasma, different electron densities in front and at the back of the mirror would result, and hence a voltage across the mirror would appear. This voltage would be built up by using the thermal energy of the electrons. Obviously, a voltage source based on thermal energy (in the absense of a temperature gradient) violates the 2nd law of thermodynamics.
I have to admit that I do not deal with details of solid state physics on a daily basis, so this is some kind of doing "armchair physics". But I would very much like to recognize the flaw in my thinking, and I didn't find publications dealing explicitely with this topic. (Usually this means that the matter is so obvious that a publication wouldn't be worthwhile.) I wrote a short paper on this subject; the quantitative result is that one could expect an open circuit voltage of the order of 200 microvolts under feasible conditions:
Any helpful comments will be highly appreciated!
PS The magnetic flux density is assumed to be limited to about 1 T (Fermi energy = 11.1 eV (iron), B = 0.5 T => path diameter = 45 micrometer), so the magnetic field can be provided by permanent magnets. Since ballistic transport is limited to low temperature, an alternative would be the use of superconducting coils.
In a laboratory setup, the entropy of the whole system would be increased by the means for cooling the device. Assuming for the moment that the effect under consideration occurs at all, a battery of such voltage sources would however, after initial cooling, keep itself cool, provided that both the thermal insulation and the electric load, located outside the insulation, were sufficient.
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Hello Stam Nicolis ,
thank you very much for your answer! I tried to avoid a question with a very long description, so I wrote just some prosa here but with a link to a text with some quantitative treatment (the graphic attached to the question shows the main result). The text also contains three sketches of possible implementations. Did you have a look at it?
The main idea is that there are two volumes of space (B0 and BM) separated by the mirror region. The boundaries of each volume are given by the borders of the metallic specimen and by the mirror. In equilibrium, the numbers of electrons crossing the mirror in both directions have to be equal which brought me to
A0 D0 P0 PA = AM DM PM PD
with the area A of the border between the homogeneous B field and the mirror region, the density D of charge carriers, the probability P of crossing the mirror based on the Lorentz force, and the probabilities PA and PD based on Pauli's exclusion principle. The indices 0 and M are referring to B0 and BM.
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Let's say we have a material AB. Is it possible to detect atomic clusters of A atoms experimentally?
The size of clusters in question: 2 atoms (nearest neighbour pairs), 3 atoms (nn triangles), 4 atoms (nn tetrahedrons).
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One possibility would be to investigate the local structure with EXAFS. Since the interatomic distance is the basic physical quantity to which EXAFS is sensitive. From the shape and strength of the changes in X-ray absorption, it can be concluded at what distance from the ionized atom it is scattered and how strongly, thus obtaining a so-called radial distribution function. From this it can be roughly estimated at what distance which or (if the atomic types of the ligands are known) how many atoms can be located there.
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Hello all,
I want to synthesize ZnO nanoparticles and PBABr in my lab for my LED project. I know the method, but I am not sure how can I check(even visually) that I have arrived at the correct result or prepared correct chemicals, If anyone could help me with that it would be great.
Thank you for being helpful with my other questions.
Jitesh
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Every metal has its own work function. if several metals are used in multilayer structures such as [Co/Ni] multilayer what will be the effect of the work function of the electrode? Can these multilayer structures change the individual workfunction?
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Peres, L., A. Bou, C. Cornille, Damien Barakel, and P. Torchio. "Work function measurement of multilayer electrodes using Kelvin probe force microscopy." Journal of Physics D: Applied Physics 50, no. 13 (2017): 13LT01.
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Hi,
I need HCI MOSRA simulation to find vth degradation. but I didn't know how to do it. especially I don't know what the constant parameters such as THCI0, TDCE, etc.
I use the following netlist to do the simulation, but the values of threshold voltage didn't change!
.model hci_1 mosra level=1
+thci0 = 5 tdce = 1 tdii = 2.7 hn = 0.5
.appendmodel hci_1 mosra nch nmos
.mosra relmode=1 reltotaltime='10*365*24*60*60' relstep='10*365*24*60*60/10'
+hcithreshold=0
+nbtithreshold=0
would you please help me with these problems?
I'm looking forward to receiving an email from you.
best regards,
Farzaneh Nakhaee
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Hi,
Did you find those parameters? If yes, please let me know about them. I really need it.
Thank you in advance,
Neha
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which is better for thin film growth, electron beam evaporation or sputtering?
which results in better film quality?
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it depends on what you want and you can manipulate the preparation condition , to get the optimum for your application
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I have seen a number of publications state that organic radicals often exhibit quenched photo-luminescence, yet offer no explanation as to why. Can someone offer a physical explanation as to why this would be the case? This question is particularly puzzling to me as you can clearly see polaronic or excitonic absorption bands in an absorption spectrum corresponding to the excitation of the radical anion. Why then does it not luminesce when excited at these wavelengths?
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All recombination mechanisms can be defined as radiative or non-radiative.
Photoluminescence measurements reveal radiative recombination processes. However, if they're intentionally or unintentionally added impurities or intrinsic defects they can form deep localized energy levels in the bandgap (gap of forbidden energies between conduction and valance bands or LUMO and HOMO). These deep traps act as efficient recombination centers according to Shockley-Read-Hall (SRH) statistics. As opposite to exciton or band-to-band bimolecular recombination, trap assisted recombination is non-radiative (usually becomes radiative only at very low temperatures in the form of additional PL peak at lower photon energy than bandgap). Since one additional non-radiative recombination path is added the photoluminescence signal is quenched because the net radiative recombination rate is reduced.
This paper is a nice example.
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Do we have a number for DOS (Nv, Nc) for 3D or 2D perovskites? Although I see few papers reporting DOS, I do not find a number. Or maybe I do not find a way to calculate DOS from the plots.
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Dear Prof. Azhar Fakharuddin ,
Last decade, it was common to use tight binding to calculate the DOS of strontium ruthenate, the first perovskite reported as been a superconductor.
Please you can look at the references within the following publication:
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You can provide links with calculation and clear examples of the methods used. I would also like to understand how to take into account a specific potential. How to determine the forbidden zone for this case. And other useful things in determining the zone structure for this case.
Thank!
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In solid states there are five 2D Bravais lattices:
1 – oblique (monoclinic),
2 – rectangular (orthorhombic)
3 – centered rectangular (orthorhombic),
4 – hexagonal, and
5 – square (tetragonal).
So my guess is that the triangular 2D lattice is part of the hexagonal one. For instance, you can check the volume V on statistical physics by Academicians Landau and Lifshitz, chapter XIII symmetry of crystals.
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How to use Wigner-Seitz cell to calculate the nearest neighbor in a given crystal? What is the physical principal? And which (free) software can be used to do this calculation?
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Dear Prof. Qingyong Ren , the nearest neighbour is given by the strongest t-hopping parameter, for example using ARPES.
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Like electronic density of states and bandstructure, we conclude bandgap, type of bandgap direct and indirect etc. Likewise what we conclude from phonon DOS ?
Any basic literature on phonon DOS and bandstructure analysis.
Any comment and conclusion on my phonon DOS plot which is attached here.
Thank You All
Shilendra
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Hello everyone,
Phonon calculations (Phonon Band Structures, Phonon DOS, and thermal properties) in materials science using VASP and phonopy are explained on the Youtube Channel. Please find the link below:
Best regards,
Rasoul Khaledialidusti
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I am aware of many femtosecond laser based approaches to excite phonon modes e.g. in crystals and minerals. Quantum Cascade Lasers (QCLs) seem like an interesting alternative, especially since they can be tuned by frequency and can be operated continuously. Has someone tried to use QCLs to excite phonon modes? Or is there a catch?
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We have setup the femtosecond Transient absorption system for nanowires or solution samples. Depending on the sample the pump may be 310 nm, 387 nm or 425 nm and similarly probe is be broadband white light continuum(350 nm-700 nm or 400 nm-750 nm. 
1. How do we know that our setup is working properly and we are getting right time constants? Is there any stable standard samples that we can use? 
2.Is the 1 arcsec retroreflector better option than using 2 mirrors in 4 ns delay stage ?
3. Please give me suggestions to improve my setup. I have attached the block diagram of my setup. 
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Using a retroreflector with low angular tolerance (<5 arcsec) is very important to make sure that the spatial overlap between the pump and probe beams is always ensured with very high precision once the delay stage moves. There are multiple samples with known transient absorption results in the literature such as graphite, gold nanoparticles, etc. I suggest that you run some measurements on one of these samples and compare to the literature to make sure your setup is working properly. However, the main measure to make sure that your setup is working properly is to measure the beam profile and pulse duration right before your sample. Not using the right optics could lead to spatial-frequency beam perturbation and/or stretching the pulse duration.
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I am currently reading some papers in the field of high Tc superconductivity. Some concepts confuse me. Can you tell me the definitions of spin wave, spin density wave, spin excitation, spin fluctuation, spin gap, charge density wave and charge order? What are the differences and correlations between these concepts? And, what their relationships with high Tc superconductivity?
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Dear Prof. Qingyong Ren
In addition to all interesting answers in this thread & for a deeply understanding of the phenomenology & the theory of spin waves & magnons---using the equation of motion of the magnetic moment & from where the concepts you mentioned (spin wave, spin density wave, spin excitation, spin fluctuation & spin gap ) were borrowed, you can studied from these books:
[1] The Nature of Magnetism by M.I. Kaganov & V. M. Tsukernik, Science for everyone, Mir-Moscow, 1995.
[2] Eletrodynamics of continuous media, L. Landau & E. Lifshitz, ch V-#48 pp 167, eq 48.2, Pergamon 1984. They use the phi thermodynamic potential free energy.
[3] Statistical Physics Vol 2 by E. Lifshitz & E. Pitaevskii ch VII Magnetism, Pergamon 1980.
[4] Spin Waves by A. I. Akhiezer, V. G. Bar'yakhtar, and S. V. Peletminskii. North-Holland & Interscience (Wiley) 1968.
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Hi all, 
I am looking for a code or package to calculate density of state in metal (Mg alloy). Previously I used VASP but it is not reliable for high energy states. Also, I see many others using VASP to calculate lattice parameters and energy, but using another code to calculate density of states.
What will you do when you calculate DOS? What's the advantages compared with VASP?
Any suggestions will be appreciated.
Thanks in advanced!
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Hi,
Step by step process of accurate (both total and projected) DOS and band structure calculations using VASP and some ways of plotting the band structure and DOS of our system is explained in a Youtube video.
The link is:
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I need information about reliability of BCS-Eliashberg-McMillan formalism especially for high Tc superconductors.
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The Eliashberg – Macmillan theory is based on the applicability of the adiabatic approximation, assuming that Ω0 << EF, where Ω0 is the characteristic frequency of the bosons, and EF is Fermi energy of electrons. In HTSC, EF is an order of magnitude smaller than in HTSC, and the characteristic frequency of the boson Ω0, apparently, becomes sufficiently large, as a result of which the adiabaticity condition may not be satisfied
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How is electron-phonon scattering treated in metals in the context of transport ? I believe that the conventional deformation potential theory used for semiconductors fails in case of metals due to the presence of multiple bands around Fermi level. Is a rigorous treatment using both electron and phonon bandstructure of metals the only way to do scattering in metals ? Or are there approximations that one can use (like deformation potential theory for semiconductors) ?
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Yes Dear Prof. Prasad Sarangapani
Electron-phonon interaction in normal metals leads to a sound attenuation effect in normal metals (by contrast to metals below the transition temperature which leads to a different calculation)
1. The classical work to study electron-phonon scattering in normal metals using physical kinetics (what you call transport) is:
Course Of Theoretical Physics Volume 10 Physical Kinetics
L. P. Pitaevskii & E.M. Lifshitz. Pergamon 1981. For normal metals see ch. IX- & 79. pp. 334.
2. The classical work about sound attenuation in normal metals is:
Theory of Ultrasonic Attenuation in Metals and Magneto-Acoustic Oscillations
Proc. R. Soc. Lond. A. B. Pippard, 1960.
(without & with magnetic field)
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solid state physics, semiconductor, materials, chemistry, quantum wire, quantum physics, band gap, energy band diagram, opto-electronics, nano devices, heater structure, indirect and direct band gap.
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Dear Prof. Amit Agarwal
For band structure calculation or energy-k calculation you might follow this general procedure more than a unique equation:
1. First, the hamiltonian of the periodic structure should be the input information (you beed to know it).
2. Second, calculate the eigen-energies of the hamiltonian at each k-point.
3. Third, plot the energy-k dispersion.
the following ResearchGate thread is very useful:
also this external link:
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CoronavirusCurrent trends in nanotechnology promise to make virus uses more diverse. From the point of view of materialists, viruses can be considered as nanoparticles. On its surface, viruses carry special tools designed to cross the host cell barriers. Viruses are commonly used in material science as scaffolds to contribute to associated surface modifications. There is a certain type of virus that can be designed from directed development. The powerful technologies developed by biology have become the basis of engineering methods toward nanomaterials, and have opened up wide areas of applications to biology and medicine. Because of their size and shape, as well as their specific chemical structures, viruses have been used as templates for organizing materials on the nanoscale. Recent examples include working at the Naval Research Laboratory in Washington, D.C., cowpea virus particles have been used to amplify signals in micro-DNA array sensors. In this application, the virus molecules separate the fluorescent pigments used to indicate blocking the formation of non-fluorescent diodes that act as dampers. Another example is the use of the cowpea virus as a nanoscale plate for molecular electronics. Is it possible for material science researchers to prepare nanocomposites that can interact with the Corona virus so that they can break down the virus into their primary compounds?
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Can you use it as a sensor?! There are reports on nanomaterials sensors! Check them out, if you wish.
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Hi, I am working on donor spectroscopy in Si. Due to low donor concentration around 10^16 cm-3, the PL signal I get by exciting 670 nm pump is very low, below noise floor. The system is locked-in already. Is there any other tricks you can share that you use for FTIR spectroscopy. I use Nicolet 8700 FTIR spectrometer with an external PL setup. The samples are in a cryostat and cooled with Liquid Helium.
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Looks like you're already doing most of the things you can do. Only other options that come to mind are "more power", if that's possible without damaging or oversaturating your sample, or collecting PL from a larger solid angle. Samples emit isotropically, the more of the space around the sample you can cover with your PL collection optics the better. E.g. you can get a parabolic mirror with a short focal length. Ultimate in signal collection is an integrating sphere, but that would be for a standalone PL setup.
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I read in Ashcroft and Mermin's Solid State Physics how only those modes that have a frequency tending to 0 as k(or q) tends to 0 contribute to specific heat capacity. This would include the 3 acoustic modes and some exceptions of optical modes. Can someone please explain this to me.
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For low temperatures, optical modes have a constant frequency independent of k, so acoustic mode contribution to the specific heat remains unchanged. We must sum over frecuencies, so it will depend upon the model for phonons that is assumed!
This link has a complete calculation for all temperatures & also for Einstein and Debye cases.
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i want to know, is it in the same way we use for a bulk system or not? If not, then what changes are required? what parameters do we look for?
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Ok Thankyou Shagun Nag
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It is claimed everywhere that PDMS can be bonded with silica-based materials, such as glass, quartz, and PDMS. I have successfully done PDMS-glass bonding with the following steps: 
1. Clean glass with Piranha and PDMS with acetone/IPA
2. Oxygen Plasma for 2min (50W)
3. Bond and cure for 15min at 90C oven
However, with the same recipe, I cannot bond PDMS with quartz. I believe the only difference is that quartz is 99% SiO2 while glass is less pure.
Is there any trick on bonding PDMS with quartz chip? 
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Hello I am interested in PDMS Quartz bonding did any of the solution work?
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As the explanation goes, hole is a figment to the absence of electron as it moves to some different energy state as a result of absorption of energy of some kind. That is, I think of holes as voids, which are "said to" have positive charge for the sake of charge neutrality because there once happened to be an electron at that place. But, it doesn't have it's own actual charge like any other physical charged particle (like an electron), right? Then, how can we define an exciton that is based on coulombic forces between an electron (in conduction band) and a hole (valence band), which actually requires presence of two physical charges?
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Dear Prof. Saransh Gupta Maybe you find interesting a reading of the following book: Quasiparticles by Prof. M. I. Kaganov, and Academician I. M. Lifzhits.
I was introduced to the topic of quasiparticles many years ago by one of the authors and I find extremely useful to read the book particularly to understand the use of the phenomenological approach of Quasiparticles in Quantum Solid State Theory. Regards.
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If we have a new sample and we do not know its space group than how we can determine it's space group from xrd pattern (2theta vs intensity) .
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In diagnostic radiography, it is advisable to carry out images in at least two projections. This is due to the fact that the x-ray is a flat image of a three-dimensional object. And as a consequence, the localization of the detected pathological focus can be established only with the help of 2 projections.
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I wish to do DFT calculations and use the frozen phonon approach via Phonopy. Should I pay attention to the magnetic moments?
Sometimes, individual atoms in a crystal have different magnetic moments. Does this have any additional effect?
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Dear Hitanshu Sachania and Franklin Uriel Parás Hernández You might take a look at the following preprint. It adresses the question of this thread. Regards.
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For the transition from insulator to metal, there have different transition mechanisms.
How to distinguish Anderson transition (Anderson insulator was induced by the disorder-induced localization of electrons) from Mott transition (Mott insulator was induced by the Coulomb repulsion between electrons. This transition can be controlled by the mechanisms of  oxygen vacancy controlled electron filling), especially in 2 or 3-dimensions materials.
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Hello,
Anderson transition is a one body problem in which localization results from quantum interferences effects. The metal to insulator transition can occur at any fiilling (carrier density) , only the strength of the disorder controls the position of the mobility edge that separates extended from localized states.
The Anderson transition does not open a gap in the one particle spectrum.
However, the Mott transition is a many body feature, that occurs at specific band filling and controlled by the strength of the coulomb electron-electron interaction. At the metal to insulator transition, in contrast to Anderson transition a finite gap opens in the charge spectrum.
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I need to calculate the barrier height of the Schottky contact based on thermionic emission theory, so i want to know the Richardson constant value for indium oxide.
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The Richardson constant is expressed by
A* = 4 pi q m* k^2/h^3,
All what do you need is to search for m* of indium oxide and the the values of the physical constant and then you can calculate the Richardson constant.
The value for A= 120 A/cm^2 K^2 for m*=m0
For the derivation of the Richardson constant please refer to the book in the link:
Best wishes
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To calculate the saturation current of the metal/ZnO/Si heterojunction diode which one should be considered for the Richardson constant. For example, whether we should consider the Richardson constant of ZnO or Si.
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The Richardson constant depends on the effective mass of the emitting material. In case of Metal to vacuum one uses the effective mass of the metal as the metal is the radiating substance in the vacuum. IN case of M-S contact the Richardson consatnt will be that of the semicondcutor because the emission occurs from semicondcutor. This concept can be applied on and heterojunction with thermionic emission. The material which controls the emission is the material which imposes the the effective mass in the Richardson consatnt.
To see the origin of the Richardson constant please see the book in the book in the link:
Best wishes