Superconductors - Science topic

Hello,

My name is Radu Jubleanu, I am PhD student at the Politehnica University of Bucharest. I work in the field of magnetic storage in superconductors, I studied some works related with superconductors , and I have a confusion related to the magnetic anisotropy of them.

More precisely, I would like a clarification, related to parallel and perpendicular magnetic fields. I saw that there are Jc curves as a function of B. But it is not clear to me who is B. Who produces this external magnetic field?

Thank you!

sorry, this got a little bit long....

Herein I want to reinitialize the scientific discurse again.

The Physicist Evgeny.Podkletnov

The experiment has never been reproduced yet,

In the 2020s the necessary technical equipment should be creatable.

But this experiment seems to be completely forgotten in the conscience of the scientific community.

- knowledge in Experimental-Physics,

- knowledge in Theoretical Physics like: QM, Spin-Physics, Bloch-Theorem,

additionally

- Electrodynamics

- basic knowledge about General Theory of Relativity

=>--- see below for the target of this discussion ---

The measured effect lead in the eyes of the writer of these lines to completely over-excessive pressure on the involved scientists. Mr. Podkletnov was not allowed to finish his experiments and a try to publish the document failed due to in my eyes unjustified overreaction of the "scientific world". Other involved Physicists suffered by damage in scientific reputation.

In the end the measurement results landed in the corner "Fringe-Physics".

The Authors bond the experimental measurement to a theoretical explanation,

that was out of bounds for serious mainstream science.

The given hypothesis has been:

"Shielding of Gravity by the rotating superconducting disc (Antigravity)"

My approach is the following

====== ====== ====== ====== ====== ====== ====== ====== ======

The unique experimental setup based on

Mr. Podkletnov reported the observation

Seen from a science-historical view, the "only mistake" that was made by the scientist Podkletnov and collegues

to hand out explanation directly together with his experimental results.

It was interpreted as a gravitational shielding.

====== ====== ====== ====== ====== ====== ====== ====== ======

in total 3 experiments have been conducted.

Mr. Evgeny.Podkletnov constructed and built a Spark-generating apparatus, working at slightly reduced pressure chamber. The observed (obviously) unusual spark-stream between a superconductor and the opposite plate indicated in the horizontal direction.

A short horizontal-impulse correlated to the spark direction and the timing was observed.

The impulse has been described to be large enough to push a standing booklet from the table. (!!!) The apparatus is labelled Impulse Gravity Generator (IGG) by its creator.

# Target of this discussion group #

These experiments started more than 2 decades ago, and have been forgotten.

Herein, the writer of these lines

tries to restart a sober SCIENTIFIC discussion on the PHYSICS of the observation.

- is to start a CONCISE and scientific discussion about the PHYSICS ,

- trying to find possibilities to reproduce the three Podkletnov-Experiments,

- to develop a theoretical approach

- suggest new experimental setups

a side task

- will be to simply collect any hypothetic reasons "of the physical background" and to categorize these by plausibility and experimental provability.

I start this discussion group at www.researchgate.net,

as I have

Additionally have an initial idea/clue,

- Respectful, friendly and adequate ways of communication is expected.

Not accepted:

- claims this (shall||must) not be a topic of ANY discussion are not followed

- completely nuts contributions about application of the effect are not accepted(e.g. Antigravity Space-ship drives).

---

Mit freundlichen Grüßen,

Dipl.-Phys. Frank Haferkorn

Is vortex state usefull for any mechanism.If so where it is employed .

If I want to simulate the superconducting magnetic shielding in the cosmol, I only need to use the complete diamagnetism of the superconductor. How should I set the superconductor?

In the BCS theory the pair density depends on temperature, meaning that pairs can be created/annihilated by temperature variations. On the other hand, in some experiments the supercurrent, once excited, runs for many months, indicating that any pair recombination doesn’t take place (pair recombination would dissipate the initial momentum of pairs). Can we solve the contradiction?

Imagine, in a mercury ring (superconductivity below T_c=4.15 K) we establish a persistent supercurrent. Then we organize temperature cycles (T-cycles) in the cryostat, say from 3 K to 2.5 K and back. According to the BCS theory of superconductivity, the pair density decreases at warming, i.e. a not negligible fraction of pairs annihilates; the same fraction of pairs emerges back at cooling. Annihilated pairs lose their ordered supercurrent momentum on the atom lattice, so the supercurrent decreases at warming; newly created pairs do not experience any electromotive-force (EMF), since the EMF is no longer available in the ring. Hence, according to the BCS theory, the supercurrent must decrease at every T-cycle and dissipate after a number of T-cycles. However, in all experiments the supercurrent remains constant and, thus, the pair recombination (assumed in BCS) doesn’t take place (note, every cryostat device produces not negligible temperature fluctuations, so every observation of long-lived supercurrents is the experiment with T-cycles).

Do the pairs really recombine in the eternal supercurrent? Do someone know direct experiments for the temperature dependence of persistent supercurrents?

Solving this contradiction of theory/experiment we can unambiguously confirm or deny the BCS theory. So far nobody explained this paradox.

Superconducting electron pairs occur on the Fermi surface, where the electron kinetic energy is a few eV. The binding energy of paired electrons is usually a few 10^-3 eV, so the electrons seemingly cannot remain paired. However, pairs are stable until thermal fluctuations destroy them. Is the situation paradoxical?

The thermal energy, destroying the superconducting gap, may be considered as energy of pair breaking. In other words, that is the energy, which the electron pair absorbs for breaking. The absorbable thermal energy of particle (here the electron pair) depends on the number of independent motions (degrees of freedom) of the particle. The factor 3.5 corresponds to a free particle with cylindrical symmetry, vibrating along its own cylinder axis. Does it mean the factor 3.5 of the thermal pair breaking is a thermodynamic consequence from the real-space-configuration of the electron pair?

It is well known that non-zero negative exchange energy indicates that a singlet state of electrons is energetically more favorite than a triplet one. Sufficiently strong thermal fluctuations destroy any magnetic spin order, so singlet and triplet order becomes equiprobable in the crystal. Hence below a certain temperature (say T*) the energy gain of the singlet order may be larger than the destroying thermal energy, and then preferred singlet pairs become stable. Thus the pairing energy is the difference between two energies:

E1. Energy of the stable singlet;

E2. Energy of the state without spin ordering, where singlet/triplet are equiprobable.

Note: we consider conduction electrons, i.e. electronic wave packets are much larger than lattice constant. So the result is not related with antiferromagnetic order.

This simple logic shows the electron pairing can be derived only from the non-zero negative exchange energy. Feel free to comment or to correct the result.

Philips and Siemens recently developed and commercialized the magnetic resonance imaging(MRI)with a liguid helium free superconducting magnet respectively. I suppose they must use a conventional superconductor such as Nb alloys, as the magnetic coil in the MRI. Is it possible to make Nb alloy be superconducting in the absence of liquid helium?

Most conventional theories of superconductivity (SC) use the second quantization notation (SQN) where all electrons are assumed indistinguishable, every electron can take every state in the momentum space. However, a sample shows that SQN is insensitive for supercurrent description.

For clarity we consider only 4 electrons (which may belong to arbitrary many-body system): a non-dissipative singlet pair (e1,e2) and two normal (dissipative) electrons e3, e4 . We investigate two cases, A and B:

A. The non-dissipative pair (e1,e2) is permanent. Then an initial non-zero momentum Px of the pair is also permanent. Obviously, this permanent Px is a supercurrent;

B. The non-dissipative pair (e1,e2) is not permanent, i.e. a recombination is possible: e1, e2 become normal, e3, e4 become non-dissipative and back. But at every time moment there are one non-dissipative pair and two normal electrons:

(e1,e2)singlet + e3 + e4 <=> e1 + e2 + (e3,e4)singlet

In case B the initial non-zero momentum of the pair (e1,e2) dissipates, because the electrons e1,e2 become periodically dissipative and there is no external force to give to the newly created pair (e3,e4) exactly the same momentum Px, which the pair (e1,e2) had. So the momentum Px of the system dissipates and the current vanishes. Thus non-permanent pairs cannot keep a supercurrent (otherwise the momentum conservation law is violated; the atom lattice took the momentum Px of the broken pair e1,e2, hence Px of the new pair (e3,e4) must be zero). Notable is the fact that both cases A and B are identical in SQN due to equal occupation numbers (in both cases there are exactly two normal and two SC electrons). However, the case A is superconducting and the case B is dissipative. The cause of the paradox is the indistinguishability of electrons.

Thus the SQN principle of indistinguishability of particles is insensitive to the supercurrent description, we should consider the normal and SC-electrons as distinguishable, i.e. non-exchangeable in the momentum space particles.

So far nobody could plausibly reconcile this paradox and conventional theories of SC.

Dear R^G 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 T_c ~ 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 T_c ~ 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.

Why do not all materials become superconductors when they cooled, while some materials show negligible resistance to current when they cooled below a temperature known as critical temperature?

Even there are some materials that are defect-free but do not shows superconductivity at low temperatures.

We measured the magnetization M=M(T) at 50 Oe (ZFC) of a superconductor. It shows a clear drop around 3.9 K and saturates at a certain value, indicating the occurrence of the expected Meissner effect. We know that not all the sample is in this state below 3.9 K. Is it possible to calculate an approximate value for the effective superconductive volume? Thank you in advance!

Dear R^G Professors, Researchers and Graduate Students:

Will be set up new sound (elastic transversal) [T100] velocity experiments regarding the time symmetry broken-state observed in the elastic constant C₆₆=C_xyxy of Sr₂RuO₄?

I mean sound velocity experiments as accomplished by Prof. Lupien et al. (2001) because there are going strain related experiments, but no sound speed ones. This is not a question on shear related experiments only.

It is a more complicated question on the ---sound transversal elastic velocity ---which is theoretically given by the real part of the polarization operator. Please see the pdf slide attached below. Thanks to all in advance.

Time-reversal symmetry broken states discovered by mean of elastic constants experiments are of tentative relevance.

Dear Colleagues,

I am in problem in measuring the transition temperature of a Superconducting sample.

I am getting absurd behaviour.

I am using four probe method with a disc type pellet.

Is it not possible to do the experiment by circular disc?

Please suggest.

Thanks and Regards

N Das

I am currently doing a project where I am making a curved electromagnetic track so that a superconductor can flux pin along it, moving wherever each solenoid is activate(where ever the magnetic field is present). In order to do this, I want to figure out how to calculate the force at one point around the magnetic field and compare it to another to figure out the optimal spacing between each row of solenoids on that curved track.

A newest Nature paper E. T. Mannila et al, "A superconductor free of quasiparticles for seconds" https://www.nature.com/articles/s41567-021-01433-7 shows that superconducting (SC) pairs persist at least for seconds. The measurement device detects single pair-breaking-events for a large pair population, so the average life time of each pair is much longer than a few seconds (probably, many hours). Thus, every pair hosts its electrons a long time. In most SC-experiments worldwide, the measurement time is much shorter than the life time of the long-hosting SC-states, therefore we can assert that the SC-electrons and normal electrons are non-exchangeable during the measurement, i.e. the SC-electrons do not hop into normal states (at least during the resistance measurement). If so, then the SC-electrons and normal electrons are distinguishable and the superconductor has two distinguishable electronic components: (i) SC-electrons; (ii) normal electrons.

Each of the distinguishable components has its own set of quantum states, its own one-particle-wavefunction, its own Fock space, although the components are overlapped in the real space.

Mainstream theories of superconductivity (BCS etc.) operate within one electronic component and don't take into account this distinguishable 2-component-nature. Should the theories be updated according to the newest finding ?

I have to introduce complex impedance spectroscopy and complex electric modulus spectroscopy before explaining plots of these. So anyone expert at this platform, please help me instantly. especially I need to know proper way of explaining attached image, related impedance.

I have one Si coating with very thin NbTiN. I coated AZ1512 as protective layer prior dicing. Because the film look not uniform so I spray acetone to remove that resist layer. What make me confuse was not only the acetone but also the NbTiN also was removed. I did look to the literature but have no clue that can happen. So my question is how to remove AZ1512 from NbTiN without peel it off?

If we make a hollow tube and create vacuum inside, than apply negative voltage on the wall - what will be the movement of electrons inside when we apply voltage at the ends of this tube? Is it not ideal superconductor?

The BCS is based on the concept of Cooper pairs (or pairons), which was actually conceived before the BCS. The concept of pairons is widely known and accepted even from researchers who think the BCS is not adequate to describe all types of superconductors. In the BCS, pairons are though to form from singlet electron pairs (with single state and total spin=0) whose total momentum is zero (-k, +k). Is there any cause that prevent triplet spin electrons (with 3 states and total spin=1) to form pairons or even other combinations of multi-pairons in superconductors?

The buzz across the energy world is the switch to "electrification" and the difficulty of creating a stable grid with just solar and wind power sources. The problem vanishes if we had a room temperature superconductor. We could run a bus around the world to smooth out power flow. How about it?

Bismuth based superconductor Bi2223 Tc-110k

Fe-based superconductors all have Fe-anion trilayer structure.

What is the role of anion in iron-based superconductivity?

Experimental setup and procedure for the measurement of Tl-2212 thin film superconductor?

MR scanner magnets are made of four types of electromagnetic windings: 1) The main magnet, made of superconducting material, creates a variable magnetic field; 2) X coil, made of a resistive material, creates a variable magnetic field, horizontally, from left to right, across scanning tube; 3) Y coil creates varaing magnetic field, vertically, from botom to top; 4) Z coil creates varaing magnetic field, longitudinally, from head to toe, within scanning tube.

Superconductors, which create the main magnetic field, should be cooled by liquid helium and liquid nitrogen.

The superconductors used exclusively are: niobium-titanium (NbTi), niobium-tin (Nb3Sn), vanadium-gallium (V3Ga) and magnesium-diboride (MgB2). Only magnesium diboride is a high temperature superconductor, with a critical temperature Tc = 390K. The three remaining superconductors are low temperature.

Dear all, I would like to build a track of NdFeB magnets to demo the Meissner effect of a superconductor, i.e., magnetic levitation. However, I am not so sure how to properly align the magnets. Below I assume a bar magnet with magnetic poles looks like [N S]. Is the following design correct?

[N S][N S][N S][N S][N S][N S][N S][N S][N S][N S]

[S N][S N][S N][S N][S N][S N][S N][S N][S N][S N]

[N S][N S][N S][N S][N S][N S][N S][N S][N S][N S]

What I want is that the superconductor can move on the track and it will not fall off the track.

Many thanks in advance!

We are studying the proximity effects between NbN superconductor (SC) and Bi2Se3 topological insulator (TI). The TI was coated first, then partially covered and the SC was coated. We are doing I-V studies by biasing voltage and measuring the current. The biasing is across the entire heterostructure (bilayer + bare TI), while the current and voltage drop across the SC are measured locally through leads on the SC. The measured voltage drop across NbN (on top of Bi2Se3) is very small compared to the bias voltage when NbN (on top of Bi2Se3) is in superconducting state. This is understandable. My doubt is, should we plot the current and the dI/dV with respect to the applied bias or the measured voltage drop? Since we obtain the superconducting energy gap from the value of voltage on the x-axis, I want to know if the x-axis voltage should be the applied bias V or the measured voltage drop across the superconductor.

I wonder if BCS theory for superconductors can persist or not.

I have gone through the paper by Davide Innocenti et al. [J Supercond Nov Magn, 24_1137 (2011)] where they provided the information about the shape resonance at Lifshitz transition in multiband superconductors. Is there any proper explanation for the superconducting TC enhancement or TC decrement with the presence of Feshbach resonance /shape resonance in superconducting materials? If yes, then is it always related with the multiband nature of superconductivity or can be apply for single band superconductors also.

The magnetic field of the main magnets of the MR scanner is created by superconductors, which need to be cooled by liquid helium and liquid nitrogen. The characteristics of the current solutions are: 1) high specific weight of the material from which permanent magnets and limited natural resources are made, 2) main magnets made of superconductors should use cryostat, with cooling vessels with liquid helium and liquid nitrogen, thermal insulation and other protective elements magnet system. Can main magnets be made using room temperature superconductors to eliminate the need for a cryostat? This would simplify the manufacture of the main magnets, and reduce its dimensions and weight. The superconductors used exclusively are: niobium-titanium (NbTi), niobium-tin (Nb3Sn), vanadium-gallium (V3Ga) and magnesium diboride (MgB2). Only magnesium diboride is a high-temperature superconductor, with a critical temperature Tc = 390K. The three remaining superconductors are low temperature. Newly discovered superconducting materials are not used in MR scanners. Why? What needs to be done to use the newly discovered high-temperature superconductors to build an MR scanner?

I have measured the value of Thermopower and Hall carrier concentration. experimentally. I want to calculate the DOS effective mass of the sample. Please explain step by step procedures...

How the high Tc superconductors divided into two separate levels depending on their doping mechanism that is electron and hole doped? How this doping happens in superconductors?

Which systems show decrease superconducting transition temperature with increase in applied pressure?

Hi All,

I am having hard time calculating force between a type I finite superconductor and a finite size magnet. Any help will be much appreciated !

Regards,

Nabin

Due to the almost isotropic character of their electronic properties, heavy fermion materials are low temperature superconductors. Organic materials should not have a high Tc either. Furhermore, good metals (Au or Cu..) are not superconducting because electron-phonon interactions can be very weak . They should have very low superconducting transition temperatures. However, since they are not single crystals, structural disturbances break their possible superconducting states. All this is it due to Fermi level positions in the wave vector space ? or may be to energy bands or both the two ?

As it has been understood, BCS theory is suitable for common metals that have almost isotropic physical properties. So, isotropic materials are probably the low temperature superconductors.

Consequently, is the anisotropy of the superconductor the key to achieving superconductivity at high temperature ?

I know that a superconductor gets spin polarized when proximity coupled to a insulating ferromagnet, and this is a strong effect, possibly killing superconductivity in s-wave superconductors. However, I want to know if there is any particular feature in the superconductor that favors this strong effect.

If there isn`t any particular feature in the superconductor, is this effect (zeeman splitting due to proximity coupling) also strong in semiconductors? Can you show me examples where this happen?

I`m looking for both theoretical and experimental explanations.

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?

Ferromagnetic ordering breaks the time-reversal invariance irrespective of nature and type of ferromagnetic ordering. Does anti-ferromagnetic ordering also breaks the time-reversal invariance irrespective of nature and type or one can observed breaking of time-reversal symmetries in some AFM state (Like Neel State) and its preservation on other states?

In AFM state, is staggered magnetization only responsible for time revers symmetry breaking or any other intrinsic effect can also lead to time revers symmetry breaking?

In the ferromagnetic state, where the magnetic moments have spontaneously chosen to point in one particular direction, time reversal effect inverts the magnetization, so it would have a microscopically-observable effect. We thus say that ferromagnetism breaks time-reversal symmetry. What about AFM (M =0), is time-reversal symmetry broken in all case just because of change of sign of their staggered magnetization due to time reversal effect or time-revers symmetry breaking will depend upon type and nature of AFM state.

Conventional superconductors are robust diamagnets that expel magnetic fields through the Meissner effect. It would therefore be unexpected if a superconducting ground state would support spontaneous magnetics fields. Such broken time-reversal symmetry states have been suggested for the high—temperature superconductors, but their identification remains experimentally controversial.

I need information about reliability of BCS-Eliashberg-McMillan formalism especially for high Tc superconductors.

The widely used formula for determination of penetration depth from lower critical field is

Hc1 = φln(k)/4πλ^2

which is valid for k>>1, Can anyone help how to find the λ for k~1 material. The mentioned formula does not give any result as the Hc1 4π λ^2 vs λ and φln(k) vs λ curves do not intersect. I know the coherence length from Hc2.

Are there any good comprehensive review article on qubits? As in, one that gives a whole summary of all the possible platform and compare their strengths and weaknesses, like trapped ion, superconducting qubits, nuclear spin, quantum dots,etc.

In Comsol, there are only two types of default boundary conditions

1.Impedance Boundary conditions

2.Perfect Electric Conductor (PEC) boundary conditions

None of the above is useful for simulating the interaction of quasiparticle in HTS and RF field.

How I can do this simulation? Is anyone is already done? Or suggest some ideas

Thanks in advance

Samples are superconductors.

I'm trying to sputter NbTiN using the AJA system (target is made of NbTi). But the plasma is never stable during the sputtering, I tried switching from DC to RF sputtering and I have the same issue (taking into consideration the different pressure that is needed for ignition).

Usually, the ignition step works well but once the system reaches the desired power and the shutter is opened, the plasma stays for 3 minutes in the best-case scenario.

I tried to sputter NbTi (to prevent nitridization of the target), but still have the same issue. What can be checked or changed in the system/ process to produce stable plasma?

In a 2D model of a high-temperature superconductor wire in COMSOL, a pointwise constraint can be added to a point on the circumference to include the current passing through the superconductor wire. In similar 3D model, I have used the same method but I got error.Please take look at screen shots.

I would be appreciate if someone can help me out .

Although magnetic impurities break time-reversal symmetry and suppress the superconductivity, there are plenty of reports on magnetic impurities on 2D superconductor or the surface of 3D superconductor (usually induced by proximity effect).

I'm curious about the feasibility of magnetically doping in the bulk without eliminating the superconductivity. If this scheme has been achieved, would anyone offer me a paper on it?

I would like to ask if it makes sense to make Tauc Plots (either Direct or Indirect band gap ones) for a material that the literature claims to be a superconductor.

Supposing that I had obtained a reasonable value (about 1.5 eV) for one of the type of Tauc plot. What would be the meaning of this band gap obtained? Is it still the gap energy between valence and conduction band?

Some additional information: I got the Tauc plot from absorption spectra of a suspension of the material, at room temperature. And the critical temperature for this superconductor according to literature is about 4.4 K.

Thank you so much for your attention

Hello, every one, Please let me know the experimental evidence for finite size effect, proximity effect and pauli paramagnetic effect in a single layer of superconducting thin and thick films from temperature dependence of the upper critical field for type two superconductors and how to relate these effects with anisotropic magnetoresistance. The discussion will be very help full for me to understanding the important phenomena involved in that material. Thanks in advance

Hi

I want to enter the conductivity of superconductor in cst but according to this paper, it is complex and depend on the angular frequency of incident terahertz wave. how can I do it?

thanks for your help

The exponential increase in the heat capacity of a superconductor

As we know superconductivity arises in BSCCO sample due to excess oxygen atom, but how do I create that excess oxygen in pure BSCCO sample by solid state reaction mechanism?

We know that the intermediate state can be observed in Type-1 superconductor and the mixed state can be observed in Type-2 superconductor. But i doubt if there is a superconductor have both of the two features? Any assumption can be considered here.

The aim of the proposed research is to improve the irreversibilty behavior and critical current density of MgB2 superconductors via chemical route. please references are welcome.

Is it possible to increase the conductivity of semiconductor using the mechanism of superconductor (Cooper pair)? and how?

Kindly provide the contact who is synthesizing YBaCuO superconductor in bulk form....

In weakly linked superconductors current Biasing results in Josephson Effect and voltage bias give Coulomb Blockade and Bloch Oscillation; but with condition of Impedance > R(Quantum).

But how the functionality of Josephson Junction changes in current biasing and Voltage Biasing?

Let say Impedance < R(Quantum) so no Coulomb blockade and Bloch Oscillation. So how the junction functionality change in voltage and current biasing?

I have a multi-filamentary superconducting tape; i.e, superconducting filaments embedded in a silver matrix. I apply an external current which I increase in a parametric sweep. I've tried to make the superconductor conductivity dependent on the mean current density inside the filaments but I don't know how. I create the function for the conductivity dependence of the superconducting filaments but I don't know how to link this dependence with the mean current density inside the filaments.

Thanks in advance.

Andy Scott.

thank you in advance ...

Can i use a specimen with dimension of 3x3x25 mm3 (thicknessxWidthxLength) for three point bending test for flexural strength. The material of specimen is ceramic (YBCO superconductor).

The electrical conductivity (sigma/tau) of a non-centrosymmetric superconductor (Tc=4.5 K) obtained by BoltzTraP shows step-like behavior.

Thanks in advances!

Critical current is one of the important properties of superconductors. So, how to calculate or estimate the critical current density of superconductor room AC susceptibility measurement.

According to Gurevich [A. Gurevich, Physica C 456, 160{169 (2007).] Upper critical field for multiband SCs in any point of Hc2(T) diagram is [mostly] defined by a single band with highest Hc2. But is it possible to derive (or was it done already?), which band it is for FeSe? All i know is that Large gap opens in Gamma point hole-band. But i am not sure how to confirm whether this band holds the highest Hc2.

For most of the superconductors, (in my knowledge) the Pauli Limited upper critical field (H_p(0) = 1.86*Tc) is always greater than the orbital limited upper-critical field (H_c2^orb (0) = 0.693*Tc*(dH/dT)Tc) . Is there any example of superconductor having greater H_c2^orb (0) than H^p(0). Please mention some references from where I can get some physical explanation about these limited upper critical values.

For a superconductor with a negative curvature in Hc2 Vs T plot we can fit the data by Werthamer–Helfand–Hohenberg (WHH) theory for spin singlet state. For a deviation from the standard spin singlet behaviour one can think of spin triplet behaviour and is confirmed by fitting the data with a p-wave superconductor.

Whereas, for a positive curvature of Hc2(T) near Tc one has to go beyond WHH theory and the feature can be explained by taking into account an effective multi-band model for superconductors. Now how to confirm, whether, the superconducting state is spin singlet (s-wave) or spin triplet (p-wave)?

Peak Effects in YBCO Superconductors.

I am doing a project on Superconductors and have to work on the condensed matter physics of it. I am starting from the basics. So I need to study Anderson and Hubbard model. I am not finding any good material on the net which explains from basic. Can someone please upload some basic material.  I am a B tech 2nd year student.