# 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.

1,300 questions
Filter by
Sorted by
Tagged with
45 views

### 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-...
1 vote
18 views

### 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 ...
• 11
1 vote
63 views

### 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 ...
1 vote
26 views

### 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 ...
• 155
21 views

### 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 $V_\text{gap} = 2\Delta / e$...
• 2,171
1 vote
50 views

### 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 ...
• 890
44 views

### 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) ...
• 11
1 vote
74 views

### 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 ...
• 162
1 vote
16 views

• 13
22 views

### 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 ...
• 109
1 vote
24 views

### 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 ...
1 vote
66 views

### 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 ...
41 views

• 919
52 views

### 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 ...
• 1
22 views

### 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 ...
• 2,511
39 views

### 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 ...
• 2,511
1 vote
17 views

### 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 ...
• 2,827
22 views

### 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 ...
1 vote
30 views

### 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, ...
• 99
1 vote
28 views

### 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 $B$ ...
• 2,827
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 ...
149 views

### 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 ...
• 1,540
1 vote
48 views

### 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 ...
• 2,827
1 vote
49 views

### 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. ...
• 11
85 views

### 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 ...
39 views

### 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, ...
• 2,827
1 vote
40 views

### 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 ...
• 2,827
27 views

### 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 ...
• 101
77 views

### 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-...
1 vote