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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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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Question about superconductivity

A long cylinder of radius $R$ is made from two different material. Its radius $r<r_0$ $(r_0<R)$ part is a material with superconducting transition temperature $T_1$, and its $r_0<r<R$ ...
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Is the uniqueness theorem correct in superconductivity?

There is an uniqueness theorem in electromagnetism. It says that the solution of Maxwell's Equations is determined uniquely by boundary conditions. We can treat superconductivity as a completely ...
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Are there topological non-trivial states in zero dimension?

The periodic table of topological insulators and superconductors suggests that there can be topological non-trivial phases in zero dimension in non-interacting system with certain symmetries. A 0D ...
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BCS Theory, Physics behind it

I am going through the mathematical steps of BCS Theory, but somehow I can't get the physics. What is the physics behind Bogoliubov transformation, how can I visualize what is happening there? Can ...
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What is a d + id superconductor and why does it break time reversal symmetry?

There are a lot of publications dealing with d-wave and d + id superconductivity, but I found no satisfying answer what exactly makes a superconductor d + id and why they break time reversal symmetry. ...
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Why do liquids exist? [on hold]

This post asks why matter exists in three phases. Most of its answers explain the existence of liquids with some variant of the following: liquids happen when thermodynamic conditions, temperature ...
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Four point probe method under liquid nitrogen

I was trying to measure the resistivity of the YBCO superconductor (but not like a resistivity- T diagram, but only at liquid nitrogen boiling point), so I needed to put the sample in thermal contact ...
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How is superconducting coherence length measured in experiment?

In a superconductor, the coherence length measure the mean distance between two electrons in the Cooper pair. How is the coherence length experimentally measured?
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Do magnets also attract super conductors?

If a superconductor can be repelled by a magnet (or, well, locked in a certain position by the magnet) can a magnet be attracted to a superconductor. What would happen if you take a peace of metal, ...
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What kinds of behavioural anomalies can a zero-field-cooled (ZFC) / field-cooled (FC) split indicate?

If a material shows a spiltting in the ZFC and FC curves, is it necessarily superparamagnetic, or could there be any other reason for the irreversibility? I have heard spin glasses also show ZFC-FC ...
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Eddy currents in a superconductor

Just had a lesson we just had our teacher introduced the concept of eddy currents, and showed us how a magnet moves slowly through a metal tube due to the opposite generated magnetic field. If you ...
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Why is the frame dragging effect trillions times as strong around a spinning superconducter?

It´s a bit of a forgotten experiment, but why measured Tajmar and his team a frame dragging effect in the surrounding space of a spinning niobium superconductor, that was even measurable in the lab? ...
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Synthesis of Fe-based superconductors

Polycrystal cuprate superconductors are generally prepared by solid state reactions: Starting reagents are in powder form, they are mixed to each other and placed into furnace on high temperature ...
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Superconductivity in graphene with spin orbital coupling, is it proper to let the order parameter on two sub-lattice equal?

I am reading this article: Edge superconducting correlation in the attractive-U Kane-Mele-Hubbard model. Considering just the first part of the article, where a negative-U Hubbard model with the ...
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Cooper pairing from repulsive potential

Suppose the Hamiltonian of a many-electron system consists of a potential which is repulsive : $\langle k_1, k_2 |\hat V |k_1',k_2' \rangle > 0$ where $k_1, k_2, \cdots$ are possible momenta that ...
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Magnetic moment of superconductors

How would a superconductor's magnetic moment be affected when it is placed in an increasing magnetic field? I know that as the magnetic field gets stronger, fluxons begin to penetrate into the ...
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Quantum levitation (locking) 3mm thick disk could carry 1000kg small car claim

I watched this TED presentation: http://www.ted.com/talks/boaz_almog_levitates_a_superconductor.html It is about superconductivity and quantum levitation. It tells that super-thin, three-inch disk ...
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Super conductivity and energy gap in fermionic/bosonic subspaces

I am trying to understand the phenomena of super-conductivity from a broader level. What I understand for now is that for super-conductivity to be possible in a system, a necessary requirement is that ...
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Cocepts regarding BCS Theory of superconductivity and Cooper pair

I have a little conceptual doubt about the BCS theory of superconductivity. A visual model of the Cooper pair attraction has a passing electron which attracts the lattice, causing a slight ripple ...
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Bogoliubov transformation with two pairing terms

Let us assume that we have a Hamiltonian of the form: $$ H = \sum_{k,\sigma,s}\epsilon_{\sigma s}\left(k\right)c_{k\sigma s}^{\dagger}c_{k\sigma s} + \sum_{k,s}\Delta_{0}\left(k\right)c_{k\uparrow ...
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How much damping is there being exerted on a vertically stable magnet moving across a superconductor surface?

I'm thinking of a flat magnet with opposite poles on the wide ends, though perhaps some other arrangement is more stable. Assuming such a magnet is levitating in a completely stable state and is ...
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Magnetic field interaction energy term

I am trying to derive the Ginzburg-Landau free energy for superconductors, and I follow most of it apart from the introduction on the term containing the magnetic field. This is the bit I don't ...
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Why is superconductance not observed at regular ambient temperatures?

I have done some reading on superconductance and understand that the reason it happens is due to the formation of Cooper pairs resulting from the attractive momentary charge concentration resulting ...
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can superconductors and other meisner materials be used as magnetic shielding in space to protect diamagnetic artificial gravity of 45 teslas?

I have seen people referring to Geim's floating frog that a human in 45 Tesla's would be held to the ground from diamagnetism above them. A very real but crude artificial gravity using powerful ...
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What do we know about the strength of the electron-phonon coupling in high-temperature superconductors?

I would like to clarify the situation of the electron-phonon coupling in high-temperature superconductors (or considering only the cuprates). The main question is what do we know about the strength of ...
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Why is the symmetric phase in a Bose gas not superfluid?

In the theory of superfluidity in weakly interacting Bose gases, one finds that in the symmetric phase the exctitations have the dispersion relation $\omega = \frac{k^2}{2m}-\mu$ with gap ...
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Majorana bound states in the Bogoliubov-de Gennes (BdG) formalism

I have the Kitaev chain tight-binding Hamiltonian into the BdG formalism (like the one in the "Bulk-edge correspondence in the Kitaev chain" section of Week 1 of this course ...
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Boundaries in superconductors

In quantum mechanics we have the famous example of a particle in a box. The finite size of the System leads to a quantization of the momentum of the particle due to the Formation of standing waves in ...
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How to write BdG Hamiltonian in graphene?

In Beenakker's paper:Specular Andreev Reflection in Graphene, the BdG Hamiltonian is written as: $$ H_{BdG}=\begin{pmatrix}H-E_F&\Delta\\ \Delta^*& E_F-H\end{pmatrix} $$ from equation (1). ...
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Equation for Electric and Magnetic field from the equation for a “massive photon”

I was reading the Quantum Field Theory book by Maggiore. There he says that in side a superconductor the photon satisfies the equation $$(\Box+m^2)A_\mu=0$$ Then he adds that the electric field and ...
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Nambu notation and the Majorana bound state

In celebrated work of Fu and Kane they show appearance of Majorana bound state thanks to presence of superconductor and surface states of topological insulator. They write Hamiltonian $H = ...
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What does it mean lattice softening and stiffening?

Which kind of proceedings does it pretend? And why it is applied to examine high temperature superconductivity?
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Supercurrent dynamics

I was trying to explain the dynamics of a DC current in a superconductor -- for example, a ring -- and was asked, essentially, Cooper pairs are the charge carriers, are all in the same state, and ...
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Higgs mechanism on a brane- application to a 2d superconductor

In usual three-dimensional superconductors the would-be Goldstone mode is eaten up by the electromagnetic gauge field via the standard Higgs mechanism. I am thinking now about a problem of a ...
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How Cooper pairs conduct curent [duplicate]

we know that electrons in superconductor are coupled somehow (How does Cooper pairing work?) creating quasi-particles called cooper pairs which are Bosons and going to ground state ( do not obey ...
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Bogoliubov-de-Gennes (BdG) formalism

Suppose you treat the mean-field BCS superconductor Hamiltonian $H$ in "BdG style" by re-writing it as $H = \frac{1}{2} \sum_k \psi_k^{\dagger} H_{BdG} \psi_k$ where, in terms of original ...
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What is “Quantum Levitation”?

I just found this video Controlled Quantum Levitation on a WipeOut Track and I'm having a hard time finding the term "Quantum Levitation" used except in reference to the video. What is the proper ...
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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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How is Meissner effect explained by BCS theory?

Someone says we can derive the GL equations from BCS theory, which can explain Meissner effect, but I want a more clear physical picture of this phenomena.
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Nesting in Fe-based superconductors

Many studies about iron-based superconductors mention the nesting of Fermi pockets, such as here or here. As far as I understand it it represents some kind of interplay between different Fermi ...
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Tabletop Synchrotron

When I was undergraduate student I asked to my proffesor why nobody has made a synchrotron machine with a superconducting circular wire and magnetic field to accelerate electrons properly and to ...
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A Proto-theorem about superconductivity

Background There are two key assumptions which are used in the Ginzburg Landau model, in light of the BCS Hamiltonian on a 2-manifold $\Sigma$: $$H_\text{BCS}=\int_\Sigma D_i\psi^\dagger D^i\psi\, ...
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Is it possible to do absolute magnetic field (flux) measurements using a SQUID?

In DC squid operation, the SQUID is usually flux-locked into a position on the flux-voltage curve, and the change in supercurrent required to maintain that lock point is used to determine changes in ...
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Current induced in concentric superconducting loops

Suppose you have two superconducting loops, concentric, in a plane. Also suppose that their radii, $R_1$ (outer) and $R_2$ (inner) have the same order of magnitude (so you can't assume $B$ through the ...
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Can current be induced in a superconductor?

Moving a magnet close to a conductor induces a current. If it consists of a superconducting material with resistance $R=0$, then my textbook says: Then the induced current will continue to flow ...
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On tests of topological superconductivity

What experimental procedures determine if a superconducting crystal (say 2D i.e. layered material) is a topological superconductor/not?
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Nambu-Goldstone bosons from a quantum anomaly symmetry breaking?

We know that: Nambu-Goldstone bosons come from Goldstone theorem: a spontaneous (continuous)-symmetry breaking of the system leads to massless scalar modes. quantum anomaly: is the anomalous ...
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TQFT's as effective theories of the groundstate subspace

I often hear: "The degenerate groundstate subspace of a QFT is often a TQFT". I'm trying to work out an example of this for, say, superconductors: In the context of condensed matter physics, the ...