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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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To ensure that there is no $E$-field inside the superconductor and Faraday's law holds true the surface current seems to eliminate its cause, why?

In a Faraday's induced EMF experiment with a superconducting loop, the current at the surface of the superconducting loop creates a magnetic field that nullifies the magnetic field created by the Bar-...
SURYABARTA SAHA's user avatar
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Finding the phase difference in Rf-SQUID [closed]

In my solution I have assumed that $\phi_{12}$ and $\phi_{ab}$ are gauge invariant. This gives me a final expression where I need to insert the flux, which I set equal to $LI$. I'm unsure which ...
Sara's user avatar
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How can I build a superconductor at home?

How can I make a superconductor at home? I have been interested in making one from scratch, but I have no idea where to begin. I have heard about YBCO superconductors and I feel as though that is the ...
newton_kisser's user avatar
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Is it possible to have a system that show superconducting behavior in magnetization and insulating behavior in resistivity? [closed]

Is it possible to have a system that show superconducting behavior in magnetization measurements and insulating behavior in resistivity measurements? if yes then please provide some references? In ...
Rick Andy's user avatar
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Josephson relations when $V$ approaches the superconducting gap

The standard Josephson relations are $I = I_0 \sin(\phi)$ and $V = \phi_0 \dot{\phi} / 2\pi$. However these equations break down when $I$ exceeds $I_0$, or when $V$ exceeds $V_\text{gap} = 2\Delta / e$...
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Is Number Operator a Generalized Momentum?

In superconducting circuit, the number operator, $\hat{n}$, and phase operator, $\hat{\varphi}$ are conjugate pairs. Is $\hat{n}$ the canonical momentum, conjugate momentum, and also generalized ...
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Significance of the phase of the condensate as compared to that of the regular Fermi sea in the Anderson-Higgs mechanism

I do not fully understand how the phase of the charged Cooper pair condensate is different from the phase of e.g. the Fermi liquid in a regular metal. The state of the metal (any quantum state really) ...
Rooky's user avatar
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Superconducting ground-state and Higgs mechanism

I found this article on spontaneous symmetry breaking in superconductors. Using the same arguments as Weinberg, the author demonstrates that the properties of a superconductor are the consequences of ...
Jean's user avatar
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Interpretation of spectral function for Anomalous Green Function

This question assumes we have quasi-particles which can be diagonalized by a BV transformation (here I am using imaginary time and I am in position space): $$ \hat{c}_{i\sigma}(\tau) = ...
scruby's user avatar
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How to derive the ODE from the EOM of vortex?

In the Lagrangian mode we have the equation of motion \begin{align} \partial_\mu F^{\mu\nu}&=j^\nu. \\ D_{\mu }D^{\mu}\phi +\mu^{2}\phi-\lambda(\phi^{*}\phi)\phi &=0. \end{align} Since we ...
Qian-Sheng's user avatar
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Do superconductors have an inner magnetisation?

When applying a magnetic field to a (type I) superconductor, the $B$-field vanishes in its interior. Often I read that the inner $H$-field does not vanish due to the magnetisation of the ...
Fabian's user avatar
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Why does the magnetic field penetrate inside the superconductor?

why does the magnetic field penetrate (that is exponentially decaying over the thin region) inside the superconductor? Does it actually contradicts Meissner effect?
Rick Andy's user avatar
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Why there is a difference in the volume fraction of a superconductor when you do measurement in Field Cooled (FC) and Zero Field Cooled (ZFC) mode?

Why there is a difference in the volume fraction of a superconductor when you do Field Cooled and Zero field cooled? What does that difference indicate?
Rick Andy's user avatar
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Why the resistance in superconductors is zero? [duplicate]

Why the resistance in superconductors is zero? I know the BCS cooper pair formation but why in principle it behaves like that?
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Will every material with strong electron-phonon coupling ($\lambda > 1$) have polarons?

Does polaron formation need only strong electron-phonon coupling? Or does it need something else?
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Derivation of the number operator in the energy basis of a qubit

I am trying to model the capacitive coupling of two transmon qubits. I would like to write the number operator in the energy basis, currently, I am working on using $$ \hat H = \hat H_1 + \hat H_2 + \...
Frostman's user avatar
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Why are zero-modes preserved on turning on coupling in twisted bilayer graphene model?

In the paper https://arxiv.org/abs/1808.05250 on page 3, they talk about how when the parameter $\alpha$ in the Hamiltonian in Eq. (5) equals $0$, we get zero modes at the Dirac points K and K’. This ...
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Tenfold way symmetry classification for systems with pseudomomentum

For classifying Hamiltonians $H(\vec{k})$ of topological insulators/superconductors in the tenfold way, one has to see whether the Hamiltonians obeys (disobeys) symmetries of the following type (let's ...
Dave Force's user avatar
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Density of states of BCS superconductor and the transverse NMR relaxation time $1/T_1$

I am trying to calculate the spin susceptibility of BCS superconductors at finite temperatures. It's well known that for conventional superconductors, the transverse NMR relaxation $1/T_1$ exhibits a ...
Jeffery Wang's user avatar
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Connection between superconductivity and breaking of $U(1)$ symmetry in superconductors

$\newcommand{\Ket}[1]{\left|#1\right>}$Suppose I have a total Hamiltonian $H = H_0 + V$ given by the usual kinetic term $$H_0 = \frac{\hbar^2}{2m} \sum_{\mathbf{k}, \sigma = \uparrow, \downarrow} \;...
OutrageousKangaroo's user avatar
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A "Classical" Explanation of The Meissner Effect?

I know that the Meissner Effect is fundamentally quantum, but can a similar logic to the one used for normal conductors be applied to superconductors? I am referring to the idea that in normal ...
davidaddisonsenjaya's user avatar
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How is the coupling between order parameter and strain determined from symmetry?

In the article Ehrenfest Relations for Ultrasound Absorption in Sr2RuO4, Sigrist M., Progress of Theoretical Physics, Vol. 107, No. 5, May 2002 A superconductor with proposed p-wave pairing and ...
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Induced current in a superconductor

I was recently solving a problem from Jaan Kalda's handouts; Parallel to and at a distance $h$ above the surface of an infinite planar superconductor is an infinitely long straight wire with current $...
Cognoscenti's user avatar
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Why is a bosonic condensate not easy to be scattered in a superconductor? [duplicate]

Why does an individual fermionic electron scatter off lattice defects easily while the Cooper pairs are insusceptible? I know they condensate to a same macroscopic quantum state, but still, why can ...
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Can one experimentally confirm whether the effective attractive interaction is retarded and its relation with superconductivity?

It's widely believed that in convential BCS superconductors, only after taking the retardation effect into consideration the weak attractive interaction mediated by phonons can overwhelm the strong ...
Black Monolith's user avatar
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Superconductor Cube levitating in Vertical magnetic field

Suppose there's a Magnetic field in vertical direction and we hold and release a superconductor cube so experimentally it is seen that the cube floats/hovers in the same orientation as it was released ...
Macron's user avatar
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Is there a way to quickly change the current in a superconducting loop?

In rocket designs such as VASIMR, superconducting nozzles are frequently used to focus the resulting plasma jet. This leaves out the question of TVC control mandatory in chemical rocket engines, and ...
Meatball Princess's user avatar
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Can real-space-eigenstates of conduction electrons in crystal cause formation of electronic singlet pairs?

Crystals may contain electronic real-space-eigenstates as ground states, which are spatially much larger than one unit cell, such as impurity states, standing waves at Brillouin zone edges, Anderson ...
Stanislav Dolgopolov's user avatar
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Why do some superconductors have a large $λ$ but a low $T_c$? Is it because mass renormalization dominates in these systems?

We know some superconductors have a large λ, but a low $T_c$. Some have a small λ but a high $T_c$. Why are they different? From the Eliashberg equations, we know the renormalization function is ...
ming xia's user avatar
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Difference between single-gap and multigaps superconductor?

We know some supercondutors show multi-gaps feature in superconducting energy gap (for example, two gaps in the MgB2), but other are singe-gap. Why they are different? Under what circumstances will ...
ming xia's user avatar
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Expectation Value of the BCS Hamiltonian

I want to calculate the expectation value of the BCS Hamiltonian $ H = \sum_k E(k) c_k^\dagger c_k - \frac{V}{2} \sum_{k,q} c_{k+q}^\dagger c_{-k-q}^\dagger c_{-k} c_k $ in the state $| \Psi \rangle = ...
ConanFromChester's user avatar
2 votes
2 answers
185 views

What is the equivalent of Slater determinants for superconductors

Suggestions to better formulate my question are also highly appreciated. To better explain my question let me start with a very familiar case: Suppose we have a two-band insulator described by $$H = \...
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Second harmonic of Josephoson current

The expression of Josephson current including the second harmonic between two s-wave superconductors is $$ I_{J}=I_{1}sin(\phi)+I_{2}sin(2\phi) $$ I try to calculate $I_{2}$ by following derivation in ...
Hui's user avatar
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What are the conditions according to which the levitation force between a magnet and a superconducting material tends to zero?

According to this article, for a disk-like superconductor and a magnet, if the radius of the superconductor tends to zero or the radius of the magnet tends to infinity, it seems that the levitation ...
Mohammad Javanshiry's user avatar
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2 answers
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How great is the net force exerted on a superconducting material of a small size being subjected to an external uniform magnetic field?

Assume that we have a very tiny spherical or disk-like superconducting material that is subjected to an externally uniform magnetic field. I want to know if the net force that accelerates the ...
Mohammad Javanshiry's user avatar
1 vote
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Would flux tubes be prevented from passing through a sufficiently thick superinsulating layer?

Suppose you have a type-2 superconducting cube with a thick superinsulating layer passing through the middle of the cube; visualized below with (grey superconducting mass, violet superinsulator in ...
Sidharth Ghoshal's user avatar
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What is the supercurrent operator in superconductivity Hamiltonian

For a U(1) symmetric Hamiltonian, the current operator can be derived simply by taking the time derivative of the density operator. I wonder how can one obtain a supercurrent operator for U(1) broken ...
rbwang's user avatar
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What is nematic phase in superconductors

I've seen the picture of nematic phase in liquid crystals like this one https://saylordotorg.github.io/text_general-chemistry-principles-patterns-and-applications-v1.0/s15-08-liquid-crystals.html, ...
L L's user avatar
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Assuming vortex defect pinning is equal, and number of tubes are equal should longer flux tubes lead to stronger pinning?

Suppose you have two superconductors that resemble rectangular prisms with identical width and length. The first superconductor call it $A$ is shorter than $B$ visualized below: Now both $A$ and $B$ ...
Sidharth Ghoshal's user avatar
2 votes
5 answers
134 views

How would current be distributed among two parallel paths of zero resistance?

In an ideal circuit with two wires in parallel, if one path has zero resistance and another has a nonzero resistance, all of the charges will flow through the wire with zero resistance (if I ...
Blob Ross's user avatar
4 votes
1 answer
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Inconsistency in microscopic derivation of the Josephson effect?

My question is related to, but different from, other questions in this platform (see this, this and this). One of the few places I have found in literature that provide a microscopic derivation of the ...
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If you embed an extremely thin magnetic strip in superconducting block do supercurrents form around the strip?

Given a superconducting block (lets assume type 1) in grey below and a very thin magnetic strip with a simple magnetic dipole structure (in blue below) inserted into the block. If we were to cool the ...
Sidharth Ghoshal's user avatar
1 vote
0 answers
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Physical meaning of the terms in the Mattis-Bardeen Integrals

Mattis-Bardeen Integrals The Mattis-Bardeen integrals for the complex conductivity $\sigma = \sigma_1-j\sigma_2$ of a superconductor describe the electromagnetic response to a high frequency drive. ...
D H's user avatar
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How can I can solution to BCS gap eq. around critical point $T_c$?

The BCS gap equation is $$1=gn\int_0^{\Delta\epsilon} d\epsilon \frac{1}{\sqrt{\epsilon^2+\Delta^2}}\tanh\frac{\sqrt{\epsilon^2+\Delta^2}}{2kT}.$$ At the critical point, we have $\Delta=0$, therefore ...
st zhang's user avatar
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Are there thermodynamic reasons a super diamagnet cannot exist?

We define a super diamagnet as a substance which not only expels any internal magnetic fields but actually produces a stronger internal magnetic field in the opposite direction of the external field, ...
Sidharth Ghoshal's user avatar
1 vote
0 answers
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Does electric charge have any effect on diamagnetism?

Diamagnetic materials repel magnetic fields because freely moving electrons or cooper pairs within the material can form eddy currents in response to a changing magnetic field. It is natural to wonder ...
Sidharth Ghoshal's user avatar
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Current in a Superconducting Loop Interrupted by a Josephson Junction

Assuming we have the following circuit consisting of a superconducting loop having the same superconductor material everywhere, and interrupted by the short Josephson junction J1 with a phase ...
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Anderson Higgs mechanism and superconducting phase fluctuations

In the context of superconductivity, in the Anderson Higgs mechanism (see, for instance, https://doi.org/10.1119/1.5093291 (PDF), or https://doi.org/10.21468/SciPostPhysLectNotes.11 (PDF), the gauge-...
evening silver fox's user avatar
1 vote
1 answer
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Are there any known bulk superinsulators?

I recently learned about superinsulators. Basically materials which exhibit an abrupt phase transition to becoming perfectly resistive. The wiki article reveals that this phenomenon is exhibited in ...
Sidharth Ghoshal's user avatar
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1 answer
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How much liquid nitrogen is required for Maglev trains?

I understand magnets require cooling to achieve supermagnetivity. How much of liquid nitrogen do Maglevs carry with them? How much is required to keep them cool? What is liquid nitrogen consumption ...
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