Condensed Matter Theory

Condensed Matter Theory

  • Manuel Morales added an answer:
    Is the Standard Model incomplete in light of String-Net theory?

    I have a doubt regarding String-Net theory. Prof. Xiao-Gang Wen stresses upon the point that all fermions must carry gauge charges. The Standard Model contain composite fermions that are neutral for U(1) × SU(2) × SU(3) gauge theory. So, according to string-net theory the Standard Model of particle physics is incomplete, and the correct/complete model should contain extra gauge theory, such as a Z_2 gauge theory. But, Coleman-Mandula theorem states, more or less, that space time symmetries (which determine spin) cannot mix with gauge symmetries in anyway. The Haag-Lopuszanski-Sohnius (HLS) extension of this theorem states that the only possible loophole to the Coleman-Mandula theorem is SUSY, as far as I understood. So, is the Standard Model incomplete from the point of view of string-net theory or is string-net theory radically inconsistent with what we see in nature, and must therefore be wrong in its present form? Also, is it meaningful to call something a Z_2 gauge theory (because, as far as I understand, discrete symmetries can at best act as "large" gauge transformations)? PS: To get an understanding/gist of what Prof. Wen is saying (as I mentioned in the first half of my question) please refer to this paper:

    Manuel Morales · Institute of Prephysical Research

    "Experiments are the judges."

    Oh really? Think again...

  • Yatendra Singh Jain added an answer:
    Is the condensed matter theory at the dead-end or are there new breakthroughs?

    Condensed matter theory had known spectacular advancement in the second-half of the last century. In the present century we only read papers where the old ideas of the last centuries are being repeated or brought to ab-initio numerical calculations? Am I perhaps too pessimistic? Please elaborate the situation.

    Yatendra Singh Jain · North Eastern Hill University

    Dear Daniel,

    Thanks for your public congratulations.   This is highly encouraging as it comes as a first public recognition for the fact that my theories have potential to explain the phenomenon of superfluidity/ superconductivity and related properties.  Your statement that your opinion is with low value expresses the politeness of the person in you, otherwise your achievements in the field of your expertise speak of the strength of your words as an expert physicist.   I sincerely believe that your words would have catalytic effect and many more physicists would believe in the accuracy and viability of of my theories.  

    Once again I express my thanks for your kind words and valuable opinion.        

  • Tauseef Anwar added an answer:
    How to calculate lattice constant from XRD spectrum?
    Lattice Constant formula.
    Tauseef Anwar · Tsinghua University

    d = a/sqrt(h^2+k^2+l^2)

    Did this formula works if I want to find lattice constant a for body centered tetragonal for TiO2 anatase phase.In lattice constants a=b but c is different. all angles are of  90. the peak for which i wanna calculate have (101) miller indices.... 

  • Claudia Bojorge added an answer:
    How can I cut glass substrates for coating?

    I make thin films and I use glasses as substrate. A single grid's dimension in my evaporation system is 16mm x 6mm. I work in 10-6 Torr vacuum.

    How can I cut my glasses with rectangular geometry?

    Claudia Bojorge · Institute of Scientific and Technological Research for the Defense

    To cut glass you can try using a diamond tip, marking the glass once, firmly (do not re-emphasize the scratch!!) and pressing hard as Thomas said.

  • Sergey Mikhailov added an answer:
    Can condensed matter theory predict ahead of the experiment?

    Condensed matter theories are notorious for not being able to predict  spectacular results/effects before the experiments were done. What they often do is to rationalize experimental results that are already known. I agree that there are a few exceptions to this rule. The brilliant exceptions are: (1)  Josephson effect, (2) Abrikosov flux lattice, (3) fractional quantum Hall effect etc. Are there many more of such brilliant theories in condensed matter physics? Can you please elaborate? Even BCS theory is useless to predict and find a new superconductor! In contrast theories like Newtonian mechanics, quantum theory and relativity showed spectacular predictive power and often the experiments were only done well after the prediction. Of course condensed matter theory is hardly fundamental in that sense and is actually applied quantum mechanics (not everyone will agree) of many particle systems.

    Sergey Mikhailov · Universität Augsburg

     I disagree. First, the fractional quantum Hall effect was not predicted before the experiment. Second, there have been many predictions which have been successfully confirmed later.

  • Jorge Quintanilla added an answer:
    What is the "minimal" accepted tight-binding description of the normal-state band structure of the iron-based superconductors?
    I am thinking in particular of modelling the band structure of Ba(Fe 1 − x T x ) 2 As 2 ( T = Co, Ni, Pd).
    Jorge Quintanilla · University of Kent

    Thanks Massimo. I guess by "minimal" I meant that it would be good enough to describe the structure of the superconducting order parameter / pairing potential - not necessarily to describe the normal state properties...

  • What are the best models for manipulating nanocomposite materials?

    I want to know what are the best candidate models that are expected to achieve some success in manipulating the mechanical and thermal and electrical properties of nano composite materials? 

    What are the difficulties that face the researchers in this field?

    Chinedu Ifeanyichukwu Amaechi · University of Nigeria

    Thanks for the paper unravelling modelling in thermal conductivity. I equally made an estimation of thermal conductivity using combination of kinetic theory, relaxation time approximation and Sommerfeld model. It is equally under review. But the models you mean in manipulating these properties, I dont really think I understand it.

  • Jan Engmann added an answer:
    Is it possible that the viscosity has an imaginary term?
    Is it possible that the viscosity has an imaginary term?
    Jan Engmann · Nestlé S.A.

    The most common formalism to describe dynamic responses in rheometric experiments for viscoelastic materials is in terms of a "complex modulus" G* with real and imaginary parts corresponding to conservative and dissipative contributions. Sometimes an equivalent formalism using a complex viscosity eta* is used where the role of the real and imaginary parts is reversed. Whether "viscosity can have an imaginary term" in the end comes down how general you define your concept of viscosity.

  • Sayyed Jalil Mahdizadeh added an answer:
    How one can theoretically calculate the electrical conductivity of materials?
    I'm going to calculate the electrical conductivity of some materials (like graphene) theoretically. Do you have any recommendations about suitable theoretical methods or can you suggest good references?
    Sayyed Jalil Mahdizadeh · Ferdowsi University Of Mashhad

    Thank you so much guys.

  • Behnam Farid added an answer:
    Do you have references on pedagogical derivation of the impurities self energy for FERMIONS?

    Can somebody suggest please suggest a reference for pedagogically simple and detailed but complete derivation of the impurities self energy for relativistic Dirac fermions, that one that gives  i \Gamma sign (\omega)

    thank you

    Dear Ignat, in my view the references I provided (in particular the book by Mahan) fall into the category of pedagogical texts. If the stumbling block is use of diagrams, then you should perhaps consult the book by Mattuck, A Guide to Feynman Diagrams in the Many-Body Problem. Beyond this, I have no more to say.

  • Saba Niaz Theoretician added an answer:
    Is it possible to calculate the optical absorption of INORGANIC materials with TDDFT?

    There are many papers about the optical absorption of organic or quantum dots solar cells that are calculated by Time-dependent density functional theory (TDDFT). But I rarely read papers using TDDFT to study the inorganic photovoltaic materials (Si, GaAs and so on). So why are there so little papers of inorganic materials with TDDFT?

    Saba Niaz Theoretician · University of Kashmir

    i agree with h.simchi take on organic materials 

  • Zhi Wang added an answer:
    What is the difference between commensurate and Incommensurate phases in the magnetic systems? How can we distinguish between them?
    I wish to learn the basics of commensurate and Incommensurate phases in the magnetic systems.
    Zhi Wang · Anyang Normal University

    Dear Philippe Lerch,

    I understand the "A commensurate state with a very simple picture. ". Could you explain more about the system TbMnO3 where the spins of Mn3+ ions form an incommensurate cycloidal spin spiral below Tlock = 28 k? What field in the system TbMnO3 plays the role of gravitational potential in the simple picture? and the strength of the triangular bonds ?

  • Vijayakumar Y added an answer:
    Can someone suggest some finer points that I should employ for depositing thin films using spray pyrolysis setup?
    Spray Pyrolysis?
    Vijayakumar Y · Osmania University

    go with low sol flow and high compressed air pressure

  • Aneeshkumar K S added an answer:
    What might be the reason for the hyperfine field in ferrite is in range 60-65T?


    Aneeshkumar K S · Pondicherry University

    Dear sirs...Sami Mahmood..Tapan Chatterji..Behnam Farid..

    Thank you for your valuable responses..Indeed the mistake was with me only..i was putting one wrong calibration constant and doing fitting which leads to these high BHF values...Now one problem is solved..Its your expertise helped me to solve this..

  • Leon Newman added an answer:
    Does anybody have any suggestion about graphene transfer to TEM grid from a SiO2/Si substrate?
    I am about to begin with the reported methods of graphene transfer but I would like
    to know if there is any suggestion to make this process easier or with higher yield
    Leon Newman · The University of Manchester

    Wash graphene off the silicon with a hydrophobic solvent like diethylether ( maybe even breifly sonicate for 5 seconds whiile supporting the silocon substrate), this maybe sufficient to desorb the graphene and solubilize the graphene in the organic solvent. Then dry off the hydrophobic solvent and resuspend in an appropriate amount of water/ methanol, (use a fume hood). Check for the presence of graphene via Raman spectroscopy ( you only need you use 10-2 microlitre for this). Then take 10ul of this dispersion and place on to a Carbon coated copper TEM grid (no need for glow discharge) then continue as normal and image ith TEM

  • Zijun Lu added an answer:
    How does Sir Vaughan Jones's work on von Neumann algebras and knot polynomials relate to statistical mechanics ?
    His work on knot polynomials, with the discovery of what is now called the Jones polynomial, was from an unexpected direction with origins in the theory of von Neumann algebras. But how is his work related to statistical mechanics?
    Zijun Lu · Case Western Reserve University
    Thank you all for the detailed answers. It has been very helpful.
  • Brajesh Tiwari added an answer:
    How can an irreversibility field Hirr(T) and an upper critical field Hc2(T) from transport measurements on a superconductor be obtained?
    I have resistivity data as a function of temperature at different magnetic fields. I want to know the formulas to obtain the irreversibility line (IL) field Hirr(T) and upper critical field Hc2(T) from transport measurements? Hirr(T) can be obtained from M-H curves at different temperatures. Please help me to understand these two fields.
    Brajesh Tiwari · National Physical Laboratory - India
    @İbrahim Düzgün .. Thank you so much. the references are very useful.
  • Sayyed Jalil Mahdizadeh added an answer:
    Can anyone help with volume diverges in molecular dynamics?
    I'm going to perform MD simulation on graphene oxide nanosheet. Everything is ok when I run the simulation without considering coulombic interactions but when I consider them the volume diverges. What is going on there?
    Sayyed Jalil Mahdizadeh · Ferdowsi University Of Mashhad
    Thank you dear Chin
    I think you are right, i'll try that.
  • Petar Mali added an answer:
    How can I describe a Hamiltonian for an Ising spin?
    I would like to model a spin Hamiltonian to describe a spinwave for Ising like spin. I am not sure which of these is correct. 1) isotropic Heisenberg + large single ion anisotropy H= Jij Si. Sj + Di Siz*Siz 2) anisotropic Heisenberg H= Jxij Sxi. Sxj + Jyij Syi.Syj + Jzij Szi. Szj (Jx,Jy << Jz) Are they actually different? If so, which should be used for the spin wave calculation for an Ising like spin? Thank you in advance.
    Petar Mali · University of Novi Sad
    In book "Quantum theory of magnetism" of Nolting and Ramakanth authors wrote that magnetic insulators which can be described by Ising model are DyPO4, CoCs3Cl, CoRb3Cl5.
  • Behnam Farid added an answer:
    How do athermal phonons propagate in monocrystalline Silicon at low temperatures (~ mK)?
    After a photon energy deposition, phonons propagate in the crystal. In case of isotropic material I will expect a decreased intensity of the phonon wave that goes like 1/d^2. (where d is the distance from the interaction point). However, monocrystalline Silicon has preferential axes, so how does the "geometrical" attenuation occur in this case?
    For the propagation of athermal phonons their non-equilibrium distribution function will have to be calculated. One way of doing this is calculation of the non-equilibrium phonon Green function with the aid of the Keldysh formalism. As time progresses, the non-equilibrium distribution function converges towards the equilibrium distribution function of phonons corresponding to the lattice temperature. If we consider phonons at long wavelengths (in equilibrium these would be the long-wavelength acoustic phonons), the distribution function should be isotropic for cubic crystals. The 1/d^2 decay you refer to, is natural in three dimensions from the perspective of energy conservation (the total flux must be bounded).
  • Behnam Farid added an answer:
    How does one understand how a Slave-boson mean-field approach will bias the resulting phases?
    An example of this is in Vaezi, Wen (2010), "Phase diagram of the Hubbard model on honeycomb lattice", where the superconducting phase is incorrectly favored in the small U/t limit.
    The introduction of auxiliary boson fields in the slave-boson technique enlarges the physical Hilbert space of the problem at hand (here of the Hubbard model in two space dimensions). To recover the physical Hilbert space, certain operator identities must be enforced within the framework of the slave-boson approach, a task which is accomplished only in an average way by the mean-field treatment of this approach; the decoupling effected in the mean-field treatment, replaces some operator products by their expectation values (i.e. c-numbers), thus suppressing quantum fluctuations. It follows that like any other mean-field treatment, that of slave-boson approach is bound to be of limited validity. There is an additional problem here (a problem that one also encounters in the treatment of the tJ Hamiltonian in terms of correlated fields), which is that the correlated fields not being canonical, Wick theorem does not apply and as a consequence beginning from the mean-field Hamiltonian it is practically very difficult to take account of the neglected quantum fluctuations --- the conventional diagrammatic approach is not valid, and as a result the algebraic expressions tend to become explosively large and unmanageable.

    On the question of the Vaezi-Wen paper, they are very explicit about the unreliability of the superconducting phase in the small-U limit; they state:

    "It should be mentioned that at small U limit, the Bose gas of holons and doublons becomes very dense and there is strong interaction between them. So the mean-field results are unreliable in this regime and the superconducting state is a fake result."

    The unreliability has to do with the mean-field approximation of operator identities, which neglect quantum fluctuations. For the reason specified in the above quotations, these fluctuations are non-negligible in the small-U limit. Neglecting quantum fluctuations always (to varying degree) mixes some part of the unphysical Hilbert space with the physical one, the amount of mixing being large where the neglected quantum fluctuations are large.
  • Sabih Uddin Omar added an answer:
    How can we explain the barrier height inhomogeneity in Schottky contact?
    Some researchers proposed to use gaussian. What about other solutions?
    Sabih Uddin Omar · University of South Carolina
    Please check the work by Dr. Raymond Tung. It's a generalized version of the parallel conduction model. I found it superior to the gaussian distribution model.
  • Kai Fauth added an answer:
    Can the dielectric constant of a bound electron associated with the charge density wave mode be negative?
    What does this tell us about the CDW Mode?
    Kai Fauth · University of Wuerzburg
    Negative DF can occur and is to be taken as such. If you think of the DF als square of the (complex) index of refraction (n + i*k) then a negative real part of the DF means that k>n. e/m waves are very strongly damped and cannot propagate.
  • Behnam Farid added an answer:
    Does anybody know the value of debye temperature for boron nitride nanoribbons?
    This is ~1700 K for bulk.
    You are welcome. With pleasure.
  • Vladimir Potemkin added an answer:
    Formation energy in metal oxides?
    Within DFT calculations, to obtain the formation energy of the impurities in semiconductors we need to have the chemical potential of the dopants and the rest of the atoms. If we want to substitute a Cu atom with Al in AlO, can we consider the chemical potential of Cu as the total energy in CuO, or we should just consider the total energy of Cu in metalic phase?

    I will be thankful for any clarification.
    Vladimir Potemkin · Chelyabinsk State Medical Academy
    You can use on-line computations at . Just register, upload your structure in SDF format, find physicochemical properties calculation, select "Heat capacity (specific heat)-Enthalpy-Entropy-Gibbs free energy-log(Bioconcentration factor)" software and start computations. Now they are available for free.
  • Kai Fauth added an answer:
    What are the possible applications of Nanocrystals?
    What are the possible applications of Nanocrystals? Can these crystals larger then 100nm be called nano and if so what are the challenges in synthesizing the same?
    Kai Fauth · University of Wuerzburg
    The question asked in this way is way too general to give a concise answer. If the question *is* so general then follow the advice of Wilson and study the existing literature. Applications will widely vary according to the material in question, so applications could be almost anything.
    As for a strict definition of "nanoparticle", that's different and varies with time. If there'd be a rush hunting for being the first guy succeeding in making a nanoparticle of material XY, stakes are high that the first guy getting a particle below one micron will call it "nano". It's always been like this, compare e.g. with the literature in ultrashort laser pulses. In the beginning, 0.9ns would be "picosecond" pulses, and 0.9ps would be femtosecond pulses and so on.
  • Behnam Farid added an answer:
    What is the reason for the inverse isotope effect e.g in PdH and PdD compounds?
    Inverse Isotope Effect (Superconductivity)
    Inverse Isotope Effect is in principle due to the Coulomb interaction (in materials originally referred to as "bad actors"), traditionally taken into account by means of the the so-called "pseudopotential" μ*, as well as retardation effects, both in principle accounted for by the Migdal-Eliashberg equations (in the post-high-Tc era, the possibility of the Migdal theorem, according to which vertex corrections of the electron-phonon interactions would be negligible, has been subject of much debate -- P.W. Anderson has much insisted on the failure of the Migdal theorem in the high-Tc compounds; for completeness, in these compounds the band-width of electrons being relatively small, the small parameter underlying the Migdal theorem -- the square root of the ratio of the electronic effective mass and the nuclear mass -- is not small). Anharmonicity of phonon excitations can also not be neglected. For detailed theoretical considerations, see the book Superconductivity by R.D. Parks, in two volumes (Marcel Dekker, New York, 1969). See also in particular the review article by Bill, Kresin and Wolf, cited here below (the first reference):
  • Sandip Pchoudhury added an answer:
    Can anyone help with drop coat technique?
    I have synthesized SnO2 nanopowders (40-50nm) by chemical route method. I want to make a thin film now out of that sample. What are the possible ways in which I can deposit thin film on glass substrate using the synthesized nano-sample?
    Sandip Pchoudhury · National Institute of Technology, Meghalaya
    Thank u.. Ur answers are really helpful.
  • Shielo Namuco added an answer:
    What will happen if you dope a magnetic material like manganese in a GdBCO bulk superconductor?
    Manganese has magnetic moment so I think it's magnetic moment might affect the superconductivity of the sample.
    Shielo Namuco · University of the Philippines Diliman
    I meant sample preparation of pure GdBCO and Mn will be added as composite. I have been adding MnO on the sample. I believe that MnO is insoluble to the compound so at certain concentration limit, both doping and addition will produce the same results. Also the same as its effect on the Tc of the sample.

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Condensed Matter Theory

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