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.

Filter by
Sorted by
Tagged with
50
votes
2answers
21k views

What is a $p_x + i p_y$ superconductor? Relation to topological superconductors

I often read about s-wave and p-wave superconductors. In particular a $p_x + i p_y$ superconductor - often mentioned in combination with topological superconductors. I understand that the overall ...
17
votes
1answer
7k views

Superconductor symmetry breaking

When water freezes continuous translational symmetry is broken. When a metal becomes superconducting, what is the symmetry that gets broken?
18
votes
2answers
2k views

Intuitive reasons for superconductivity

Superconductivity I read in a book "Physics - Resnik and Halliday" the explanation of Type-I Superconductors {cold ones} that: The Electrons that make up current at super-cool temperatures ...
7
votes
3answers
6k views

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 ...
11
votes
3answers
1k views

Is a superconductor really a super conductor?

It is known that a superconductor is a material with electrical resistance zero. My question is, it is exactly zero, a theoretical zero, or for practical realistic reasons it is effectively zero?
17
votes
1answer
5k views

How can I put a permanent current into a superconducting loop?

I know that you can use induction to create a current in a superconducting loop, but this only works as long as the coil that induces the field has a current flowing through it. And obviously, this ...
11
votes
2answers
12k views

Superconducting gap, temperature dependence: how to calculate this integral?

Tinkham (page 63) states that the temperature dependence of the gap energy of a superconductor $\Delta(T)$ can be calculated using the following integral: How can this actually be carried out? I am ...
31
votes
6answers
20k views

How can Ohm's law be correct if superconductors have 0 resistivity?

Ohm's law states that the relationship between current ( I ) voltage ( V ) and resistance ( R ) is $$I = \frac{V}{R}$$ However superconductors cause the resistance of a material to go to zero, and ...
12
votes
3answers
4k views

How come a photon acts like it has mass in a superconducting field?

I've heard the Higgs mechanism explained as analogous to the reason that a photon acts like it has mass in a superconducting field. However, that's not too helpful if I don't understand the latter. ...
10
votes
2answers
9k views

How does quantum trapping with diamagnets work?

I just saw this demonstration by someone from a Tel Aviv University lab. What they achieved there is mind blowing. I myself own a levitron that uses the Hall effect to levitate a magnet, the problem ...
18
votes
5answers
19k views

Is current in superconductors infinite? If they have 0 resistance then I (V/R) should be infinite? [duplicate]

I learned many years ago that according to Ohm's law, current is equal to voltage divided by resistance. Now if superconductors have zero resistance then the current should be infinite. Moreover the ...
7
votes
1answer
1k views

BCS state with well-defined particle number - interpretation?

It's common knowledge (and has been discussed in other questions on this site) that the standard BCS ground state $ \left|\Psi_{BCS}\right\rangle = \prod_k \left( u_k + v_k c_{k\uparrow}^{\dagger} c_{-...
17
votes
5answers
2k views

What is the link between the BCS ground state and superconductivity?

The link between the BCS ground state $$ \left|\Psi_\mathrm{BCS}\right\rangle = \prod_k \left( u_k - v_ke^{i \phi} c_{k\uparrow}^{\dagger} c_{-k\downarrow}^{\dagger}\right) \left|0\right\rangle $$ and ...
18
votes
3answers
3k views

Shine a light into a superconductor

A type-I superconductor can expel almost all magnetic flux (below some critical value $H_c$) from its interior when superconducting. Light as we know is an electromagnetic wave. So what would happen ...
11
votes
5answers
23k views

If a superconductor has zero resistance, does it have infinite amperage?

If amps = volts / ohms, and ohms is 0, then what is x volts / 0 ohms?
10
votes
2answers
13k views

How do superconducting materials float in magnetic field?

The movie Avatar got me interested in the subject, but so far I only found sophisticated articles loaded with unfamiliar words. Is there a simple way to explain how magnetic field affects ...
10
votes
4answers
4k views

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.
7
votes
2answers
718 views

Topology and Superconductor Symmetry Breaking

I read an article today on stack exchange titled "Superconductor Symmetry Breaking". The 2016 Nobel Prize was awarded for research on topological phase transitions in the study of superconductors and ...
1
vote
1answer
878 views

How is the current equation calculated from Ginzburg-Landau (GL) free energy?

In the Ginzburg-Landau theory, we can get the current expression from GL free energy: $$F = \int dV \left \{\alpha |\psi|^2 + \frac{\beta}{2}|\psi|^4 + \frac{1}{2m^*} \mid (\frac{\hbar}{i}\nabla - \...
1
vote
0answers
107 views

Acceleration of electrons from Cooper pairs and EM radiation

For the question What makes Cooper pairs of electrons so fit for an unhindered current through a superconducting wire? where was a nice comment from CountTo10: Assume any photons are effectively ...
24
votes
2answers
2k views

Do topological superconductors exhibit symmetry-enriched topological order?

Gapped Hamiltonians with a ground-state having long-range entanglement (LRE), are said to have topological order (TO), while if the ground state is short-range entangled (SRE) they are in the trivial ...
15
votes
3answers
8k views

Why does a superconductor obey particle-hole symmetry?

We normally solve the Bogoliubov-de Gennes (BdG) equations in order to compute the energy spectrum of a superconductor. The Nambu spinor is a common object that is used in formulating these equations. ...
36
votes
3answers
2k views

Why is high temperature superconductivity so hard to solve?

The phenomenon of high temperature superconductivity has been known for decades, particularly layered cuprate superconductors. We know the precise lattice structure of the materials. We know the band ...
18
votes
3answers
4k views

Mean field equations in the BCS theory of superconductivity

In BCS theory, one takes the model Hamiltonian $$ \sum_{k\sigma} (E_k-\mu)c_{k\sigma}^\dagger c_{k\sigma} +\sum_{kk'}V_{kk'}c_{k\uparrow}^\dagger c_{-k\downarrow}^\dagger c_{-k'\downarrow} c_{k'\...
15
votes
2answers
3k views

What does "particle number conservation" mean in condensed matter physics?

What exactly does it imply about a condensed matter system to have particle number conserved or not conserved? For example, why does the superconducting phase break particle number conservation while ...
6
votes
2answers
4k views

How does a phonon cause two electrons to attract each other and form a cooper pair?

We know that like charges repel each other. But my professor claimed that two electrons can attract each other as well. What he said was that due to screening an electron travelling at some speed won'...
19
votes
3answers
11k views

Can a superconducting wire conduct unlimited current?

A superconducting wire has no electrical resistance and as such it does not heat up when current passes through it. Non-superconducting wires can be damaged by too much current, because they get too ...
10
votes
2answers
4k views

Relativistic drift velocity of electrons in a superconductor?

Is there a formula for the effective speed of electron currents inside superconductors? The formula for normal conductors is: $$ V = \frac{I}{nAq}$$ I wonder if there are any changes to this ...
5
votes
3answers
262 views

How does the supercurrent expression $\vec{j}_s=-\frac{n_se^2}{m}\vec{A}$ arise in Coulomb gauge?

The expression of the supercurrent in a superconductor is $$\vec{j}_s=-\frac{n_se^2}{m}\vec{A}$$ where $\vec{A}$ is the vector potential, $n_s$ is the number density of superconducting carriers and $e,...
1
vote
1answer
2k views

Effect of strength of magnetic field on the height of a levitating superconductor?

Quantum levitation, flux pinning -- basically, when a superconductor floats above a permanent magnet, is really fascinating. But does the strength of the magnetic field influence the superconductor's ...
15
votes
1answer
2k views

Experimental signature of topological superconductor

I was wondering if someone can provides some clear experimental signatures of a topological superconductors ? I was thinking about that, because for topological insulator, one of the hallmarks is ...
20
votes
3answers
820 views

Why is there a band structure for strongly correlated systems?

The existence of band structure of a crystalline solid comes from the Bloch theorem, which relies on the independent-electron approximation. Why do people still talk about the band structure for a ...
13
votes
1answer
3k views

To what extent can the superconducting order parameter be thought of as a macroscopic wavefunction?

I know that the order parameter does not obey the Schrodinger equation; it instead obeys the Ginzburg-Landau equation. However, I am unclear as to the situations under which the view of the ...
14
votes
3answers
14k views

Can superconducting magnets fly (or repel the earth's core)?

If a superconducting magnet and appropriate power supply had just enough $I\cdot s$ (current $\cdot$ length) so that when it was perpendicular to the earth's magnetic field, the force of the ...
6
votes
2answers
1k views

London theory, an electromagnetic description?

Currently I'm reading "Introducton to Solid-State Physics" by Charles Kittel, 8th edition and about superconductivity. I'm having a bit of trouble getting the whole plot, because as far as I'm ...
9
votes
2answers
2k views

Goldstone modes and Anderson-Higgs mechanism in the context of BCS theory

I'm already familiar with the "Mexican hat" story of Anderson-Higgs mechanism in Landau-Ginzberg theory. However, I have never seen anyone talking about Goldstone and Higgs mechanism in the context of ...
8
votes
2answers
6k views

Why are Cooper pairs formed by electrons of opposite momentum and spin?

I understand that Cooper pair in low-temperature superconductivity are formed by electron-phonon interaction. Normally one then assumes that electrons of opposite momentum and spin are paired. This is ...
6
votes
2answers
361 views

How to understand the "condensation" of Cooper pair in BCS theory?

Condensation First of all ,what I understand about "condensation" is that: there exists macroscopic occupation in one or more than one states, i.e. there exists a state $|i\rangle$ with ...
12
votes
1answer
8k views

Why superconductors aren't used in space?

As we all know temperature of space is near to absolute zero.Then why super conductors aren't used there?
7
votes
2answers
3k views

Superfluidity and superconductivity?

Superfluidity and superconductivity? Is there any relation between the two aside from the fact that they are somewhat analogies , I see a lot of people on the internet who claim the helium (in it's ...
4
votes
2answers
2k views

Anticommutatorrelation in Bogoliubov-de Gennes Hamiltonian

I almost solved the problem Equivalence of Bogoliubov-de Gennes Hamiltonian for nanowire. In the next steps I used the notation by arXiv:0707.1692: $$ \Psi^{\dagger} = \left(\left(\psi_{\uparrow}^{\...
11
votes
4answers
13k views

Measuring the spin of a single electron

Is it possible to measure the spin of a single electron? What papers have been published on answering this question? Would the measurement require a super sensitive SQUID, Superconductive Quantum ...
6
votes
3answers
5k views

Where does the phase difference come from in a Josephson Junction?

When you separate two superconductors by a thin insulating film, a current $I(t)=I_0 \sin{\theta(t)}$ flows between the superconductors, where $\theta$ is the phase difference between the ...
4
votes
2answers
3k views

spontaneous symmetry breaking of U(1) in superconductivity

In the crystal, infinitesimal translational symmetry breaking makes the phonon, In ferromagnet, time-reversal symmetry breaking makes magnon. I know that in superconductor there is a spontaneous ...
5
votes
1answer
1k views

In superconductivity, is resistance =0?

If a metal shows superconductivity of electricity at definite temperature, then during superconductivity can we consider resistance of metal = 0?
3
votes
2answers
748 views

Charging by induction

When we charge an conductor by induction and grounding, we first bring a negative charge to the conductor. As a result the mobile electrons of the conductor get repelled and stay far from the negative ...
2
votes
4answers
5k views

What happens in a circuit, when the wire and the battery are superconducting. And shorted

When a wire with no resistance is connected to the terminals of an ideal battery, will a current exist in the circuit? If a capacitor is added to the circuit, will it be charged by the battery or will ...
1
vote
1answer
82 views

Quark pair superconductor: Even parity is favorred than odd parity

It seems that the quark pair superconductor can be odd or even parity pairing respect to the parity $P$. Say that the even parity has the form: $$ \langle\psi C \gamma^5 \psi\rangle $$ the odd ...
1
vote
1answer
274 views

Bogoliubov transformation BCS Hamiltonian

I am reading on the BCS theory and the bogoliubov transformation to diagonilize the BCS Hamiltonian. And there is one step that I really can't seem to get. So the Hamiltonian looks like this: \begin{...
2
votes
1answer
274 views

What is the 'super' parameter of superconductivity and what is the role of Cooper pair?

Only thing I know about superconductors is that here the electrical current face zero resistance. My first question is what is 'super' (physical or mathematical entity) about a superconductor. Or more ...