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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What makes a superconductor topological?

I have read a fair bit about topological insulators and proximity induced Majorana bound states when placing a superconductor in proximity to a topological insulator. I've also read a bit about ...
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Should a superconductor act as a perfect mirror?

I have been told that metals are good reflectors because they are good conductors. Since an electric field in conductors cause the electrons to move until they cancel out the field, there really can'...
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Can one define wavefunction for Bogoliubov quasiparticle excitation in a superconductor?

Wavefunction is essentially a single particle concept. It is easily extended to multiparticle system as follows- if one has say five electrons the wavefunction of this five electron state is any ...
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Topological number of 1-D p-wave superconductor---Kitaev model/wire

After learning the Kitaev model, I tried to reformulate it and encounter some conceptual loopholes of my own. Here the setting: Given the 1-D chain Hamiltonian (differed from original form proposed ...
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BCS-BEC crossover

It would be really helpful if somebody could describe what does one mean by a BEC-BCS Crossover. I was going through articles available on the topic, but I was unable to grasp the gist of the topic.
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How does current flow in superconductors if Cooper pairs have zero momentum?

I've been reading a lot of condensed matter textbooks, which state both that the net momentum of a Cooper pair in a superconductor is zero, and that Cooper pairs have momentum when they carry current. ...
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Validity of mean-field approximation

In mean-field approximation we replace the interaction term of the Hamiltonian by a term, which is quadratic in creation and annihilation operators. For example, in the case of the BCS theory, where $...
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Aharonov-Bohm Effect and Flux Quantization in superconductors

Why is the magnetic flux not quantized in a standard Aharonov-Bohm (infinite) solenoid setup, whereas in a superconductor setting, flux is quantized?
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Why do superconductors conduct electricity without resistance?

Many authors have suggested that persistent currents in superconducting rings arise from the energy gap in the single-particle spectrum. Indeed, the argument has been put forward many times on this ...
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Electric charge conservation in a superconductor

In a superconductor, $U(1)$ gauge symmetry is spontaneously broken. But $U(1)$ gauge symmetry is responsible for conservation of electric charge. Then it appears to me that the electric charge ...
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1answer
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Equivalence of nonlinear sigma model and the $CP^1$ model

While studying the non-linear sigma model, defined by the action $\mathcal{S} = \int dtd^2x (\partial_\mu n^a \partial^\mu n^a)$ along with the constraint $n^a n^a=1$, people often use the map $n^a = ...
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What is the physical meaning of phase in a superconductor?

I am trying to understand the physical meaning of phase in the order parameter of a superconductor. In particular,I was looking at this article that states the phase $e^{i\theta}$ in the BCS ground ...
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How far away are we from resolving high temperature superconductivity?

What are the major recent findings and their corresponding contributions to an overall picture? How well explained are the various regions of the dome, is there any thing that is pretty well ...
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A better conceptual model for cooper pairs in a superconductor

The conceptual model I have been introduced to for cooper pairs in a bulk superconductor is what I would call the "wake" model, where one electron deforms the positively charged lattice, changing the ...
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1answer
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Can superconductivity be understood to be a result of quantum entanglement?

I've been trying to find out what causes superconductivity. I have seen a lot about what characterizes it (e.g the Meissner effect). But I haven't found much on the root cause. The closest I have ...
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1answer
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What is the physical meaning of the particle-hole symmetry in condensed matter physics?

It is often mentioned that a mean-field BdG Hamiltonian for a superconductor has the particle-hole symmetry. i.e., if $|\Psi_{\mathbf{k}}\rangle$ is an eigenstate of $H^{BdG}_{\mathbf{k}}$ with ...
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BCS pairing and BEC pair between Fermions

In many lecture notes, it points out We can tune the scattering length, using Feshbach resonance, to realize crossover from BCS to BEC in degenerate Fermi gases. When the scattering length is ...
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Pairing symmetry / superconducting gap symmetry

I'm not (yet :-) ) an expert on superconductors, but one term I keep hearing all the time is that of the symmetry of the gap, which can be s-wave, p-wave, d-wave etc. What exactly is the symmetry ...
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Do spin-polarised Cooper Pairs break the Pauli exclusion Principle?

So far I learned that electrons of a Cooper pair should have opposite spin to account for Pauli's exclusion principle, because their other quantum numbers are the same. Is this understanding correct? ...
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Mermin Wagner theorem in superconductors, massive Goldstone mode

For a continuous symmetry breaking one receives a massless Goldstone mode which leads to divergent phase fluctuations in 2 and 1 dimension, thus we end up with a disordered state. However in ...
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Density of states in $k$ space for the BCS Hamiltonian

I would like to understand how we can find the density of states in $k$ space for the BCS Hamiltonian. First, let's talk about free electrons. When we deal with free electrons, the Hamiltonian is $\...
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What is “quantum locking”?

I've always assumed that "quantum locking" was a term invented by the writers of Dr Who, but this video suggests otherwise. What is quantum locking? Is it real?
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1answer
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Interaction strength in BCS theory

I'm looking to plot the band gap $\Delta(T)$ as a function of temperature between $T = 0$ and $T = T_c$ by numerical evaluation of the band gap equation $$\frac{1}{\mathcal{N}(0)V} = \int_0^{\hbar\...
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How is stable levitation possible?

This question is with reference to the video in this blog post: http://www.universetoday.com/90183/quantum-levitation-and-the-superconductor/ My question is the following: how is the disc stable in ...
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What do massive photons have to do with superconductivity?

I keep reading that the idea of massive photons leads to an explanation of the Meissner effect but I fail to see how photons are involved with the repulsion of fields inside a superconductor. How ...
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Superconducting wire with temperature gradient

If you have a piece of wire that is a superconductor (say Niobium), and you hold the temperature at one end above $T_c$, and the other end below $T_c$ -- would you have a state of both superconducting ...
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superconductor levitating in earth's magnetic field? [duplicate]

Possible Duplicate: Can superconducting magnets fly (or repel the earth's core)? I've seen superconductors levitating on magnets. But is it possible for superconductors to levitate on Earth ...
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What are the current contenders/most promising approaches to High Tc Superconductivity?

I want to know what kinds of things theorists are currently looking at. Specifically, I want to know more about the promise that field-theoretic methods are showing. I am studying superconductivity at ...
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Why does Pressure Increase the Tc (Critical Temperature) of a Superconductor?

Just a heads up - please make this answer understandable to around 1st year degree level physics - not PhD research. So I can understand it - thanks. I was wondering why they Critical Temperature (Tc)...
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How does Cooper pairing work?

Cooper pairs are one of the models how superconductivity is explained. What still baffles me is how a vibration of the crystal lattice (the so-called phonon) can interact with the electron (an actual ...
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What are the easiest to get/make LN2 superconductors?

I am starting to build multistage Peltier cooler at the moment, and it should be able to reach -100C at least (but if I fail I can always get boring LN2). Doing some experiments with superconductors ...
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Indefinite Number of Particles in BCS Superconductor and the Higgs-Anderson Mechanism

In general, the BCS ground state wave function can be written as $$|\psi_G\rangle=\prod_k (|u_k|+e^{i\theta}|v_k|c_{k\uparrow}^\dagger c_{-k\downarrow}^\dagger)|\phi_0\rangle $$ According to ...
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How does a massive photon arise in the Condensed Matter Analogue of the Higgs Mechanism? [duplicate]

I've tried the wikipedia pages, papers (too complex) and other forum answers on this seemingly popular topic, to no avail. Without going into too much mathematics (sorry), could someone please ...
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Reference needed for Iron-based superconductors

Iron-based superconductor is a class of high-$T_c$ superconductors discovered in 2008. Are there any review papers about these superconductors yet? If not, which are the key papers in the field?
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Lorentz force on type II superconductors?

The electrical resistance being zero in a superconductor, if a magnetic field is strong enough to generate vortices where the flux lines will pass through the material, and the current flow is ...
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1answer
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Strength of Magnetic Field Around a Superconductor

I recently learned that the strength of a Magnetic field around a conductor is proportional to the current flowing in it. So if we have a Mercury wire at absolute zero and pass a current through it (...
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2answers
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Why is there an energy gap in superconductors?

I'm a little out of my depth here... I'm trying to understand quasiparticle tunnelling in superconductor-insulator-superconductor junctions. Many books use the "semiconductor model" to explain this: ...
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Nature of Cooper pairs

Some people say it is bound state, some say it is not. Which is more accurate? Problem is that I read in some books, including Ziman, that Cooper pairs are bound states but my teacher says that it is ...
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What is the RC time constant in a superconductor?

In conventional conductors, the RC time constant is the time required to charge or discharge a capacitor through a resistor by ≈ 63.2 percent of the difference between the initial value and final ...
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Why aren't superconductors shiny? [duplicate]

Superconductors are really good at conducting electricity. Should they not reflect light very well too?
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If increasing applying energy to an atom excites electrons, why does electrical conductivity decrease as temperature increases?

Applying energy to an atom makes the electrons jump up to higher energy levels. This is known as excitation. Electrons on higher energy levels are easier to remove from an atom than those on lower ...
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BCS wave function in Neutron stars

I've heard mentioned in various classes that neutron stars, like superconductors, are described by BCS theory. I know that in superconductors a key element in forming cooper pairs is a net attractive ...
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Temperature-pressure plot for superconducting records?

Eremets et al. (arXiv:1812.01561, Nature 569, 528–531 (2019)) and Hemley et al. (arXiv1808.07695, PRL 122, 027001 (2019)) have reported new high-temperature record for superconductivity, as covered by ...
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What are gapless superconductors?

How are superconducting materials classified as gapped or gapless, also is this same as saying that a superconductor is conventional or unconventional? Could you explain how this is linked to topology ...
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What determines a state of matter?

Earlier I studied about the three states of matter-gaseous,liquid ans solid. Then, I came to know about Plasma and Bose-Einstein Condensate. Now, scientists are trying to explain superconductivity as ...
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Are photons inside the media massive? If yes, why there is no Meissner effect?

We all know in vacuum travels with speed $c$, hence its rest mass has to be 0. In the media the light speed $v<c$. Then the photon renormalized by the medium (call it "quasi-photon" if you like), ...
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Has BCS Cooper pair condensate been observed in experiment?

Feshbach resonance in s-wave scattering states a BCS Cooper pair condensation at B-field just above the resonance where the scattering length a <0. Just wondering if the condensation has been ...
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Could some astronomical objects have superconducting properties?

The colder it is, the more efficient the superconductivity process works. And as we know, if there is no star nearby, space gets pretty cold. I do appreciate that many condensed, burnt out, stars ...
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1answer
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Ampère's law and superconductors

I have been reading about superconductors and emerge me a inquietude about the explanation of existence of currents inside the superconductor while their magnetic field (inside too) is zero. Based in ...
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Superconductor general concept questions

I was thinking about building an electric motor using superconductors and I have some general concept questions in regards to how the behavior might be different from ordinary wires. The Meissner ...