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
0
votes
0answers
26 views

How to derive the wavefunction for a $p$-wave superconductor?

I would like to understand the steps for deriving the spatial wavefunction for $N$ fermions in the $p$-wave BCS ground state. In this paper, they derive the BCS ground state (Equation 11, though I ...
0
votes
0answers
24 views

How do Experimental Condensed Matter Physicsts find Interesting Material

In general, this question is "how much material science does a condensed matter theorist need to know and how do I learn?" More precisely, as a condensed matter theory PhD student, I am ...
0
votes
0answers
17 views

Josephson Junction - characteristic Impedance

Currently, I am working on antennas connected to a Josephson Junction to detect terahertz radiation. The junction shows a normal state resistance $R_n$ of approx. $0.9~\Omega$. To simulate the ...
1
vote
1answer
34 views

Superinsulator infinite voltage

Everybody knows about superconductivity, at cryogenic temperatures conductor resistance drops to zero for direct current. There is lesser known related phenomena called superinsulator where material ...
0
votes
0answers
17 views

Diagonalizing the BCS model as a Gaudin model

I've been looking at the BCS model through a few papers (listed at the bottom). I'm having trouble with many things but I think I've boiled it down to a few: -- In the first paper below (Ortiz), the ...
0
votes
0answers
9 views

Johnson noises in the Josephson junction based devices

I have difficulty understanding that superconductors being non-dissipative; have resistive noises. Even if we consider the case of charge noise and minimal thermal noises (if present) how can we ...
1
vote
3answers
99 views

Is superconductor just a perfect conductor or anything more than that?

If I had a hypothetical perfect conductor having infinite conductivity and I cool it below a certain temperature, will it be a superconductor? If not, then how can we distinguish between the two using ...
1
vote
0answers
42 views

Entanglement spectrum of a superconductor

Consider the Hamiltonian $$ H = \sum_{k} \epsilon_k c_{k}^{\dagger} c_{k} + (\Delta_k c_{k}c_{-k} + h.c.) $$ where $\epsilon_k$ and $\Delta_k$ are that of p-wave superconductor. So we have ...
1
vote
0answers
27 views

Identify symmettry in BdG hamltonian

I am confused about what symmetry is responsible for the $(E,-E)$ pairing of the energy levels in a superconducting hamiltonian. Consider the superconducting Hamiltonian $$ \mathcal{H} = \Psi^\dagger ...
1
vote
1answer
59 views

Which force causes eddy current in a perfect conductor / superconductor plane?

As far as I know, Electric and magnetic field inside a perfect conductor plane are zero (it can be proved by combination of Ohm's law and Faraday's law of induction). When there is a magnetic field, ...
0
votes
0answers
24 views

Unit Cell of Twisted Bilayer Graphene

Would anyone please tell me how to build up the unit cell of twisted bilayer graphene? I know how to rotate the coordinate of atom with a certain angle through the multiplication of a rotation matrix, ...
1
vote
1answer
23 views

Superconducting rod moving at a constant velocity in a uniform magnetic field

A conducting rod moving in a uniform magnetic field with a constant velocity is used as an example in textbooks, with charge moving from one end of the rod to the other and the amount of charge ...
1
vote
0answers
31 views

Any Books about Superconducting Quantum Computing?

I'm an undergraduate majored in physics and I'm quite interested in superconducting quantum computing. Are there any books or maybe reviews about this field (suitable for beginners)?
1
vote
0answers
30 views

Effect of Moving Charge on Current of Superconductor

Suppose you have a superconductor that is in a superconducting state and holding a constant current. If moving charges pass within the superconductor's magnetic field and get accelerated by its ...
0
votes
0answers
18 views

Magnetic field inside a superconductor ring vs a bulk superconductor

In the book by Rose-Innes, Introduction to superconductivity there is an argument that a superconducting ring of area $A$ fulfills $$ Li+AB_{\rm ext} = {\rm constant}, $$ with $L$ the inductance of ...
2
votes
1answer
68 views

Zero energy eigenstates of the Kitaev chain Hamiltonian

I am thinking about a two-site Kitaev Hamiltonian. Namely, $$H = -\mu c^\dagger_1 c_1 -\mu c^\dagger_2 c_2-t c^\dagger_{2} c_1-t c^\dagger_{1} c_2 +\Delta c_1 c_{2}+\Delta c_2^\dagger c_{1}^\dagger.$$ ...
0
votes
0answers
20 views

What is a Purcell filter?

Can someone explain, in the context of superconducting qubits, what is a Purcell filter? Several reviews mention it but I would be interested if someone explains the concept intuitively, rather than ...
1
vote
0answers
24 views

Bogoliubov spectrum of pair-density wave is not particle-hole symmetric

I am currently reading this review article about pair-density wave: https://doi.org/10.1146/annurev-conmatphys-031119-050711. There is a statement that I am not sure whether I understand. It is said ...
1
vote
0answers
17 views

Is there a difference between zero resistance and dissipationless transport?

Zero resistance in superconductors is what I have learned in university and in textbooks. But in the field of topological insulators, I have seen the phrase "dissipationless transport" get ...
3
votes
2answers
103 views

Mermin-Wagner and superconductivity

Why can superconductivity exist in 2D since Mermin-Wagner should forbit it? This question was asked here before, but I don't think anyone gave a satisfactory answer, so let me revisit it. I have read ...
1
vote
2answers
90 views

Has a true Superconductor ever been produced?

Having a conversation with a friend, we where discussing about the conductivity and resistance changes of superconductors. He insisted that available superconductors produced by universities or ...
1
vote
0answers
43 views

Diagonalizing BdG Hamiltonian for p-Wave Superconductivity

In the book Topological Insulators and Topological Superconductors by B. Bernevig, the authors introduce a 1D-chain of spinless fermions with p-wave superconductivity in Chapter 16: $$ \begin{equation*...
0
votes
1answer
35 views

BCS Theory: Bogoliubov Transformation for Fermions

I would like to follow up on this question. The Bogoliubov transformation is written as follows (I assume that $u_{\mathbf{k}} = u_k$ and $v_{\mathbf{k}} = v_k$ as well as $u_k, v_k\in\mathbb{R}$): \...
1
vote
0answers
43 views

Phase-Number Uncertainty in the extreme cases

I'm trying to understand the phase-number uncertainty relation for superconductors, \begin{align} \Delta N \Delta \varphi \gtrsim 1. \end{align} In particular, I'm trying to understand if it holds for ...
1
vote
0answers
24 views

What is the easiest way of calculating Fermi surface averages numerically?

I am interested in calculating Fermi surface averages, which are defined as $$ \langle X(\mathbf{k})\rangle = \frac{1}{N_F}\sum_{\mathbf{k}}\delta[\epsilon(\mathbf{k})]X(\mathbf{k}),\quad N_F=\sum_{\...
4
votes
1answer
88 views

Why is symmetry not spontaneously broken in superconductors?

Take the BCS model of superconductivity. We have creation and annihilation operators for the electron, $\Psi/\Psi^\dagger$, and the order parameter for the phase transition from the metallic phase ...
-1
votes
1answer
51 views

Does the superconducting current lose energy by means of radiation?

Superconducting circular currents can last for years. Don't they lose energy by EM radiation, as every circular current does? Or are there simply no lower energy levels for the electrons to fall into? ...
0
votes
0answers
37 views

How does unitarity relate $\langle \psi^\dagger \psi^\dagger\rangle$ and $\langle \psi^\dagger \psi\rangle$ in superconductors?

Let $\psi^\dagger(x)$ be the creation operator for electrons. I read an argument that a nonvanishing Cooper pair amplitude $\langle \psi^\dagger(x) \psi^\dagger(x)\rangle$ implies a diminished local ...
1
vote
1answer
64 views

Finite threshold value for two-body binding

In his book Introduction to Superconductivity, Second Ed., Chapter 3.1, when discussing Cooper's 1956 paper and the formation of Cooper pairs, Tinkham states [...] it is well known that binding does ...
14
votes
4answers
3k views

How can you measure the zero resistance in a superconductor?

As we know, superconductors have zero resistance. How can we measure the zero resistance in a superconductor? Can you devise an experiment to measure the zero value of resistance?
0
votes
1answer
52 views

Current in a supermagnetic loop after rotating through a magnetic field

A problem was given as follows: A superconducting loop of radius R has self inductance L. A uniform and constant magnetic field B is applied perpendicular to the plane of the loop. Initially, current ...
2
votes
0answers
28 views

How to measure $V \propto I^3$ behavior of $\text{NbSe}_2$ under its critical current?

Last week, I attempted to measure the superconductivity of multilayer NbSe${}_2$. As one can see in figure 4 in this paper, I expected $V \propto I^3 $ behavior under its critical current $I_c$ for ...
1
vote
1answer
24 views

Interpretation of $u_k$ and $v_k$ in BCS Groundstate

I have some questions about the BCS groundstate. This is given by $$\prod_k (u_k + v_k c_{k\uparrow}^\dagger c_{-k\downarrow}^\dagger) |0\rangle$$ I've heard many times that $|v_k|^2$ is the ...
0
votes
1answer
61 views

London equation problems

London's acceleration equation. $$E=\frac{m}{ne^2} \frac{DJ}{dt}$$ is derived from the definition of current density and $F = ma$ However, why is the magnetic contribution of force ignored for the ...
1
vote
1answer
52 views

How do Bitter magnets work (compared to a standard wound coil)?

How does a Bitter magnet differ in its construction from a simple wound coil magnet? A Bitter magnet is made from a stack of plates with holes in a helical arrangement separated by insulators. The ...
1
vote
0answers
29 views

Superconducting gap function vs condensation energy

Within BCS mean-field theory, what is the relationship between the superconducting gap function (or the superconducting order parameter $\Delta(k)$) and the condensation energy (the energy gained by ...
0
votes
0answers
30 views

Energy of Quasi-particles in a BCS superconductor

In BCS theory, we are given the energy of the quasi-particles as $E = \sqrt{\varepsilon^2 + \Delta^2}$ in which $\varepsilon = \frac{\hbar^2k^2}{2m} - \mu$, with $\mu$ being the chemical potential. As ...
0
votes
0answers
20 views

Ratio gap / critical temperature BCS

The ratio between the supercond. gap and the critical temperature is said to be equal to a constant in BCS theory. Is it true only for s-wave supcond (e.g. pairs with (spin up,k) and (spin down, -k)) ...
3
votes
2answers
73 views

How do we justify the chemical potential term in a Hamiltonian of interacting fermions?

Consider a noninteracting fermi gas of electrons. If we know the chemical potential it makes sense that the Hamiltonian is $$\sum_{|k| > k_f} E_kc_k^{\dagger}c_k +\sum_{|k| < k_f}E_k c_kc_k^{\...
0
votes
0answers
27 views

What is the role of Fermi level in a superconductor? How will you understand the Fermi level in a superconductor?

What is the role of Fermi level in a superconductor? How will you understand the Fermi level in a superconductor? Distinguish between the Fermi level of a metals and superconductors?
0
votes
0answers
31 views

Can you distinguish between different materials by looking them visibly if you have metals, semiconductors and superconductors?

Can you distinguish between different materials by looking them visibly if you have metals, semiconductors and superconductors?
0
votes
1answer
43 views

Infinite current density inside superconductor

Context: It is commonly stated (such as in Tinkham's "Introduction to Superconductivity") that the current in a superconducting wire is concentrated in a layer around the surface of ...
0
votes
0answers
14 views

Critical Field outside the Meissner limit - derivation

In Tinkham's "Introduction to Superconductivity" Second Edition, Chapter 2.2.1, the author states that ... the superconducting state becomes energetically unfavorable above the magnetic ...
0
votes
1answer
30 views

Magnetic Field at the interface and around a superconductor

In Tinkham's "Introduction to Superconductivity" Second Edition, Chapter 2.2.1, the author discusses the problem of a superconducting slab in a uniform external field. In the solution ...
1
vote
0answers
22 views

Zero of energy and chemical potential in a superconductor

I am having trouble grasping some concepts related to how energy is measured in a superconductor. In BCS theory, we are given the energy of the quasi-particles as $E = \sqrt{\varepsilon^2 + \Delta^2}$ ...
0
votes
0answers
19 views

Vector identity and Electric Field Screening in Tinkham's

I'm going through Tinkham's "Introduction to Superconductivity" Second Edition. In Chapter 2, the author states that "we obtain \begin{align} -\nabla \times \nabla \times {\bf E} = \...
1
vote
1answer
51 views

How do you translate from separate vector potential gradients to magnetic field components?

In an attempt at calculating anisotropic London penetration depths, I have obtained equations of the form $$ \begin{split} -\mu_0^{-1}\nabla^2B_x &= Z\partial_yA_z - T\partial_zA_x-Y\partial_zA_y,\...
0
votes
0answers
8 views

Why does triplet pairing not have line nodes on the fermi surface when spin-orbit coupling is present

I have read that in the presence of spin-orbit coupling, triplet pairing superconductors "in general" do not have lines nodes on the fermi surface (e.g., [1],[2]) under symmetry properties, ...
0
votes
0answers
14 views

Can phonons induce non-$s$-wave superconductivity?

In BCS theory the interaction is considered isotropic and the result is an $s$-wave superconductor. Is it possible anyway for unconventional superconductors to have SC driven by phonons (I intend this ...
0
votes
0answers
7 views

Literature on predicting overall device behaviour using component-wise simulations on superconducting quantum devices

I am looking for literature on combining electromagnetic analysis of individual superconducting quantum devices to predict overall device behaviour, for instance using tools such as HFSS

1
2 3 4 5
22