Questions tagged [superconductivity]

Superconductivity is the transmission of current with no resistive losses, and is one of the most active areas of condensed matter physics research.

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Adding an Impurity as a Perturbation to a Simulation

I am working on some plots corresponding to superconductors (of many kinds). If we insert a vortex, we can view this as an impurity and observe the Quasi-Particle-Interference (QPI). How I go about ...
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Flux linked with coil [closed]

when a super conducting loop with zero resistance is moving towards a magnetic, the flux linked with the loop is a) Increases b) Decreases c) Remains constant d) First increases then decreases
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Is there a consensus of experimental evidence amongst scientists of whether spin-charge separation exists in 2d?

I am looking for a very simple qualitative, definite answer of whether there has been a legitimate experimental evidence of spin-charge separation in 2D. This is for a presentation for one of my ...
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Superconductor behavior near absolute zero

How does critical current change for superconductors as temperatures approach the millikelvin realm, particularly High-Temperature Superconductors?
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Conditions for Bogoliubov-de Gennes Hamiltonian representation

The $H_{BdG}$ hamiltonian is described in topocondmat.org as follows: here we can see that the submatrices along the diagonal are related as negative of complex conjugate of each other, I feel that ...
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Incredible electron drift velocity in atomic thin layer of graphene?

Free electrons in atomic thin layers of graphene behave more like photons (Bosons) than fermions reaching incredible drift velocities and mobility which reach speeds as reported by this article in the ...
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Why does doping allow for Cooper pairs in high temperature superconducting cuprate compounds in Resonating Valence Bond Theory?

Preface: I'm a first years masters student (only in my second quarter) and I'm well aware that RVB theory is an extremely complex and high level topic. I have to give a presentation for one of my ...
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Momentum and position representation of BCS Hamiltonian

I am struggling to relate the BCS Hamiltonians in momentum and position representations. The free part of the BCS Hamiltonian is often written $$ H_{\text{pos}} = \int d^3 r ~ \psi^\dagger(r) \left(\...
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Why is their a penetration depth in superconductors if the Meissner effect perfectly expels the applied external field?

I’m a little confused about the Meissner effect and the penetration depth. Does the penetration depth only happen above critical values for Hc, Jc, and Tc? Does it happen in type two superconductors ...
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Ginzburg Landau model from Usadel equation

I have been learning how to obtain the Ginzburg-Landau model (local theory) starting from the Eilenberger equation (microscopic theory). I recently come across the Usadel equation which is obtained ...
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Why electrons that form the cooper pairs only lie within $\omega_D$ of the Fermi energy in superconductors?

In BCS theory, it's said that electrons that form the pairs only lie within $\omega_D$ (Debye frequency) of the Fermi energy. Why is that? Edit - In Quantum field theory for the gifted amateur, ...
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Lowering the Schwinger limit with superconductors while considering the Unruh effect?

Unruh Effect is often left out in calculations regarding the Schwinger limit. I've been looking at different mechanisms for more easily attaining the Schwinger limit. So far, the only thing I have ...
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Why is the energy of a vortex in a superconductor finite?

I just had a glimpse of the Ginzburg-Landau theory of superconductivity. I am surprised that that the energy of a vortex is finite. This is surprising because as far as I know, in superfluids, the ...
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Applying Kramers-Kronig to the real part of conductivity results in a real and imaginary term

Following Tinkham's Introduction to Superconductivity, the complex conductivity in the two-fluid approximation is defined as \begin{equation} \sigma_i(\omega)\equiv\sigma_{1i}(\omega)-i\sigma_{2i} \...
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Total Josephson current through superconductor junction with magnetic field

I am given a diagram of a Josephson Junction like so: With a magnetic field $B = \mu_oH$ in the z-direction. I'm reasonably sure $d_x,d_y,d_z$ are normal lengths, not infinitesimal lengths although ...
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Composite fields and statistics

The usual explanation for superconductivity is that the electrons form Cooper pairs, which are bosons. This effective boson then condenses. E.g., quoting Wikipedia, Therefore, unlike electrons, ...
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Why don't perpetual motion machines with superconducting magnets work?

A superconducting magnet works by energizing a superconducting magnetic coil, then short circuiting it to make a closed loop. Would it be possible to transfer the current back and forth between two ...
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London equations and flux pinning

I am having some conceptual issues with the London equations, namely the equation for the magnetic field and penetration depth. $$ \frac{d\vec{J}}{dt} = \frac{ne^2}{m}\vec{E}$$ Behavior of magnetic ...
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Why having an exponential dependence of specific heat on temperature indicate presence of energy gaps? [duplicate]

Key experimental contributions made the main properties of the superconductors more transparent before the BCS theory appeared in 1957. The observation of an exponential decay of the specific heat at ...
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Number and phase operators in superconductors

It is stated in many texts that the number operator $N$ which counts the number of Cooper pairs and the phase operator $\phi$ which counts the superconducting order parameter's phase $\text{Arg}(\...
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Is viscosity directly connected to non-superfluid component?

I am having questions when considering the microscopic models of superfluid BEC. In weakly interacting dilute alkali gas BECs, there are ways to introduce normal fluids without reducing the condensate ...
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Momentum conservation in correlation functions

In Mahan "Many particle physics" the following Hamiltonian is considered in studying electron tunnelling through a junction \begin{equation} H_t = \sum_{kp} T_{kp} c^\dagger_k c_p + h.c. \...
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Excitations of Neutral Superfluids and their Interactions

I need some clarifications about the low energy excitations superfluids and their interactions. First case, Bose superfluid: As far as I know, there are 3 kinds of commonly known excitations in this ...
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Correlation functions with different momenta

In Mahan's "Many-particle physics" p.653 the following correlation function is evaluated \begin{equation} \Phi(i\omega)=-\sum_{\textbf{k},\textbf{p},\sigma}\sum_{\textbf{k}',\textbf{p}',\...
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Why are single-electron states occupied at $T=0$ in superconductors?

Some textbooks show a density of states where the single-electron states below the Fermi energy are occupied at $T=0$ (see picture). However, I thought that at $T=0$ all electrons are paired. Hence ...
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Will I get a shock holding a superconductive wire?

Assume a current carrying superconductive wire is in front of me, with no voltage source attached. If I hold it, will I get a shock? Forget for a minute that the superconducting wire will be too cold ...
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The boundary between superconducting and not-superconducting states. Are there any observable phenomena there?

Imagine we have a long cylinder of a superconductor and we conduct the following experiment: one end of this cylinder we keep below the critical temperature, so it is in a superconducting state, while ...
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Type I Superconductors

A type II superconductor is known for how it can undergo quantum locking when below a certain temperature, but not much attention is given to type I superconductors. With some research, I found that ...
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Conceptually understanding an Ising-type transition

I am currently reading the following paper. The system consists of a chain of mesoscopic superconducting islands (aka a Josephson Junction array), but each island also contains a quantum wire that ...
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Microscopic derivation of the Josephson effect

In section 18.7 of Bruus & Flensberg the authors provide a microscopic derivation of the Josephson effect. The hamiltonian on both sides of the tunnelling junction is just the typical BCS ...
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A simple question about parallel connecting a short circuit (+the physical interpretation)

1. Introduction We know that $$1/R_1 + 1/R_2 = 1/R_t \ (equation \ 1)$$ $$\therefore R_t = \frac{R_1\times R_2}{R_1+R_2} \ (equation \ 2)$$ when $R_1$ and $R_2$ are connected in parallel and $R_t$ is ...
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What is a "lossy" cavity?

I am studying cavity electrodynamics and superconducting qubits and the term "lossy" always comes up as in a lossy mode or a lossy cavity. If the qubits are superconducting, what is "...
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Little's model for superconducting oxidized atactic polypropylene?

Little’s organic superconductor is illustrated by this picture , which is taken from this site, and by his words: “Consider an electron moving along the spine of such a molecule. As the electron ...
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Self-Consistent gap equation: numerical solution

I'm trying to calculate the simple self-consistent gap equation in Python. $$\Delta = \lambda \int_{-Ec}^{Ec} \Delta \frac{\tanh\left(\frac {\sqrt{\xi^2 + |\Delta|^2}}{2K_{b}T}\right)}{2\sqrt{\xi^2 + ...
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What is the difference between the superconducting energy gap, order parameter, and pair potential?

I often see these terms used interchangeably in literature. However, in papers that discuss the proximity effect in bilayers, I'll see statements saying the order parameter is spatially dependent but ...
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What are good references to understand how Cooper pairs transport charges in superconductors?

I am trying to get a deep understanding of superconductors (in the BCS treatment) and I am now focusing on a detailed description of charge flow in superconductors. I have managed to find some partial ...
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Gauged topological BdG systems

Can anyone suggest literature showing in detail that in 2+1D, a gauged $p+ip$ or a DIII BdG superconductor is a $Z_2$ gauge theory? I know this work https://arxiv.org/abs/cond-mat/0404327 , but I am ...
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Dielectric susceptibility and scattering intensity

I am currently reading a paper about Resonant Soft X-ray Scattering and they mentioned that the resultant scattering intensity can be found from the dielectric susceptibility of the thin film, with ...
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Why does there seem to be a disconnect between the spatial dependence of the order parameter and spatial dependence of the superconducting gap?

I am studying superconducting bilayers. My understanding is that the superconducting energy gap is the real part of the order parameter. In many theory papers describing S-N or S-S' contacts, they ...
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Expression for contribution of demagnetizing field to magnetic field in long thin superconductor with long axes parallel to magnetic field

I am reading Superconductors from Kittle's Introduction to Solid State Physics book, there while giving a brief idea about the Meissner effect, that superconductors behave as if $B=0$ inside and then ...
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Calculate the energy gap using Green's function

Can I calculate the energy gap of the given Hamiltonian by Green's function? Is there any basic code in MATLAB to do that?
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How to do a fitting with the alpha model of heat capacity for a superconductor?

I am trying to do a fitting of experimental data of heat capacity of a superconductor using the alpha model (Padamsee et al 1973), I checked Johnston 2013 as well. I am trying with the following ...
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What's the crystal orientation of this YBCO sample?

I recently purchased this YBCO crystal. The epitaxial thin film composition is described as <100> YBCO and the package it arrived in describes it as "orientation: (100) with edge (100)"...
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Bean model: Pinning force vs. magnetic? force

I am trying to study the Bean model, and as I understand, there are two forces at play. First, we apply an external field parallel to the surface, which varies in x. This causes a current density, and ...
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Why fusion reactor is not made of high-temperature superconductor?

As we know, there is several kind of high-temperature superconductors discovered. However, when I learned that current tokamaks and stellarators just mainly use Niobium-tin superconductor (which is ...
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Phase transition in 1st and 2nd Order

I was going through some texts and they said that in the absence of magnetic field the transition of super-conducting material to and ordinary conductor is a 2nd order phase transition. It also said ...
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We know electric current is the flow of free electrons,but,where do these free electrons come from?how are they seperated from the valence shells? [duplicate]

We know that electric current is the flow of free electrons,these electrons have charge and they carry electrical energy and we use this energy to do work, alright,makes sense, but,from where do these ...
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Why in superconducting cylindrical thin tube of radius $R$ the magentic field lines would be exactly parallel to the axis of cylinder?

Consider a superconducting cylindrical coil of length $L$ radius $R$ and having a current I around its mantle, (Assume that current causes magentic field which passes through the superconductor area ...
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Reference/source of the "derivation" of the magnetic force moment on anisotropic superconductor (type II)

I have been reading a diploma thesis of a fellow physics student and I have came across the following that was not referenced in any way (I want to read about it some more): The section starts... In ...
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What would be the behavior of the electric field in extremely long superconductor wires?

I have that very simple physics question. Imagine a simple Battery-resistor circuit (basic Ohm's law), but with two extremely long superconductor wires (1 light-year long, this is, 9 460 730 472 580,8 ...
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