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.
1,078
questions
0
votes
0answers
6 views
phonon-electron interaction in superconductors
Hej!
I'm trying to understand the phonon-electron interaction in supercondcutors. I'm a high student doing a project in superconductors and I can't find understandable information about it. Almost ...
2
votes
1answer
56 views
How to derive that resistivity is zero from the BCS theory?
The conventional superconductors can be explained using the BCS theory. Usually, the BCS theory is introduced as follows:
We would like to consider the Hamiltonian that describes the system of ...
0
votes
0answers
8 views
Why do we use wet oxygen atmosphere during the sintering process of ybco thin film?
We're making ybco thin film superconductor by FF-MOD method, during the formation of ybco phase in furnace, from the room temperature to 825 degrees of centigrade we use wet oxygen atmosphere, but I ...
1
vote
1answer
194 views
Inductance in Superconductors
This is a picture I got from a question in this website, it seems totally fine, but if you try looking it gain, is the heater placed in the wrong position? Because as I know current takes the path of ...
2
votes
4answers
264 views
How do we know that superconductivity is due to Cooper pairs as opposed to pairs of more than 2 electrons?
I am wondering how do we know that superconductivity is due to Cooper pairs? I.e. due to pairing between 2 electrons, as opposed to say, pairs of 6 electrons.
If a pair of electrons consists of 6 ...
7
votes
2answers
298 views
Is electricity perpetual in a superconductor system?
I wonder if electricity consumption happen according to the Law of conservation of energy and Joule effect, in a regular circuit certain amount of energy is transformed into heat by components ...
0
votes
1answer
34 views
How does a superconductor moves along a line of magnets if it's flux-pinned?
So I saw a plenty of demonstrations where superconducting piece of material moves freely along a magnetic surface, usually a line of arranged magnets, and at the same time it is claimed that flux ...
1
vote
1answer
160 views
What is the difference or connection between inverse proximity effect and triplet proximity effect in superconductors?
I know that inverse proximity effect affect the order parameter of the superconductor and that triplet proximity effect convert singlet Cooper pairs into triplets. But how is the two phenomena ...
1
vote
0answers
12 views
Is a room-temperature & pressure single-photon sensor theoretically possible?
In the realm of photonic quantum computing, single-photon sensors are required for determining the outputs of each chip. Unlike most forms of QC, photonic chips themselves may be run at room ...
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 ...
4
votes
0answers
32 views
Current State of Research on high $T_c$ Superconductors
After looking at these two RevModPhys articles, I have found myself perplexed by the current state of high $T_c$ superconductivity research. Seeing as I cannot find any SE articles more recent than 5 ...
4
votes
2answers
169 views
Relation between critical temperature and density of states
The BCS theory predicts that the critical temperature of the superconducting transition is given by
$$
T_c \approx \theta \exp \left (- \frac{1}{U D(\epsilon_F)} \right )
$$
where $\theta$ is the ...
1
vote
3answers
205 views
Would we need a battery if there was no resistance?
I'm struggling to wrap my head around this idea.
Imagine that we have a wire with no resistance ($R=0$). According to Ohm's law $V=IR$, the voltage drop ($V$) between any two points would be 0, and ...
2
votes
1answer
34 views
Are all known non-BCS superconductors doped Mott-insulators?
The question is similar to this one, where I've read with interest Mike Stone's comment. A yes or no-with-counterexample answer would be helpful.
7
votes
1answer
547 views
Can superconductivity be understood to be a result of quantum entanglement?
I've been trying to find out what causes superconductivity. I have seen a lot about what characterizes it (e.g the Meissner effect). But I haven't found much on the root cause.
The closest I have ...
0
votes
0answers
41 views
How does a superconducting qubit exists in the superposition of $|0\rangle$ and $|1\rangle$ states?
In the presentation of superconducting qubits, it is often said that a non-linear inductor is what allows the present of an anharmonic oscillator. This means that because the difference between the $|...
2
votes
1answer
142 views
Tight-binding extended attractive Hubbard model for unconventional superconductivity
BCS theory suggest that the effective attraction between two electrons, due to electron-phonon coupling, is in momentum ($k-$)space. However, in literature, (real space) tight-binding Hubbard model ...
3
votes
1answer
74 views
Why does it take hours or even days to turn on (or power up) the large, powerful superconducting magnet in an MRI machine or fusion reactor?
Sorry I can't (yet) provide any links, but I have read in the past that turning on an MRI machine from scratch can take many hours, even days, because of the time it takes to get the powerful ...
0
votes
0answers
4 views
How does force-free SMES design look like?
Recently I stumbled upon the topic of superconducting magnetic energy storage. One of the limits on the maximum amount of energy that can be stored in such systems, is imposed by the fact that ...
2
votes
0answers
42 views
Phase of BCS wavefunction
Can anyone explain to me why the phase of the BCS wavefunction
$|\Psi_\text{BCS}\rangle=\prod_\mathbf{k}(|u_\mathbf{k}|+|v_\mathbf{k}|e^{i\theta_\mathbf{k}}
\hat{c}_{\mathbf{k}\uparrow}^\dagger\hat{c}...
-1
votes
1answer
223 views
Is Meissner effect really caused by expulsion of magnetic flux?
The Meissner effect is the expulsion of a magnetic field from a superconductor during its transition to the superconducting state.
This is the explanation by mainstream physics.
But the experiments ...
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 ...
2
votes
2answers
2k views
What is paramagnetic current-current correlation?
I know what paramagnetism is. But first I want to know about the paramagnetic current and then the above-mentioned correlation?
Actually, I am working on a paper on superconductivity where I have seen ...
1
vote
0answers
23 views
Why the value of Abrikosov beta parameter is a sum of series?
The order parameter $\psi(x,y)$ can be written as :
\begin{equation}
\psi(x,y)=\sum_{n=-\infty}^{\infty}c_n\exp{(inky)}\exp\left[{-\kappa^2\over2}\left(x-{nk\over\kappa^2}\right)^2\right]
\end{...
0
votes
0answers
26 views
Having more electrons than the Fermi energy allows
What happens when we have more electrons in a solid metal than the Fermi energy and Pauli exclusion allows?
Let's say we reduce the temperature to a level where all the energy states are filled with ...
0
votes
0answers
19 views
How to calculate the value of Abrikosov beta parameter?
The order parameter is $$\psi(x,y)=C\sum_{n}\exp\left(inky-{\kappa^2\over2}\left(x-{nk\over\kappa^2}\right)\right).$$
There is a periodicity in $x$ and $y$ directions, where
\begin{equation}
\psi(x,y+...
0
votes
1answer
350 views
How to fit Werthamer-Helfand-Hohenberg (WHH) equation in a $H_{c2}$ vs $T$ equation?
The Werthamer-Helfand-Hohenberg (WHH) formula $$μ_0H_{c2}(0)=0.693μ_0T_c\frac{dH_{c2}}{dT}|T→Tc$$
was used to estimate μ$_0$H$_c$2(0) at 0 K where only orbital breaking effects are considered in the ...
0
votes
0answers
16 views
Determining the critical current density in superconductors
I am trying to determine the critical current density in a superconductor with the help of a four point probe. The instructions are the following
Set the current through the probes 1 and 4 at 0.1 Amp,...
2
votes
3answers
100 views
BCS Theory: why does $\langle \hat{\Delta}^{\dagger} \hat{\Delta}\rangle \approx \langle \hat{\Delta}^{\dagger}\rangle \langle \hat{\Delta}\rangle$?
My textbook (Advanced QM by Yuli V. Nazarov) defines the Cooper pair creation operator as
$$Z_{k}^{\dagger}=c_{k,\uparrow}^{\dagger}c_{-k,\downarrow}^{\dagger}.$$
The text then goes on to show that ...
1
vote
1answer
77 views
Why does the Meissner effect occur?
I am a high school student doing a science project in superconductivity so my physics knowledge is limitated but I have read a lot about the topic so I understand quite a bit. :)
I understand that ...
0
votes
0answers
30 views
Pressure and insulator-metal transition
Why does a seemingly large class of materials become (super-)conducting (see [1]) when subjected to strong enough pressure? The issue is discusssed for specific cases in a myriad of papers, but I was ...
5
votes
2answers
119 views
Hubbard-Stratonovich transformation without field theory
Can one do something like a Hubbard-Stratonovich transformation that decouples the Cooper channel without Field theory?
In other words, is there a sense (which can be made precise without appealing to ...
4
votes
3answers
163 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 ...
0
votes
0answers
46 views
What is "magnetic instability"?
I saw "magnetic instability" many times in papers about superconductivity, but what is magnetic instability exactly?
like this paper 10.1103/PhysRevB.40.10816 They only mentioned "...
1
vote
1answer
86 views
Integration range in BCS theory
In two different ways of finding the Cooper pair energy gap, the limits of integration are different, yet both give the same result.
In the first case, when working out the energy $E_{pair}$ of a ...
3
votes
0answers
33 views
Is the superconducting gap the same as the many-body gap in superconductor?
In conventional superconductors, it is well known that there is a gap $\Delta_{\text{sc}}$ to electronic or quasiparticle excitations. This is the gap that shows up when one measures the temperature ...
0
votes
2answers
234 views
Is there net current through a Josephson junction at zero bias?
It is widely stated that when a Josephson junction is placed in a superconducting circuit, the cooper pairs can tunnel through and create a net current without a bias voltage. However, given that the ...
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 ...
3
votes
0answers
90 views
BCS groundstate as eigenstate of the Cooper pair annihilation operator
In section 3.7 of his book Introduction to Superconductivity (2nd Ed.), Tinkham states that
[...] we note that S has the eigenvalue $e^{i\varphi}$ in a BCS state in which the the phase of $\Delta$ [.....
2
votes
0answers
37 views
$\rm Cu_2O_3$ and cuprate HTS
According to English Wikipedia Cu2O3 “is a hypothetical inorganic compound”, which “has not been isolated as a pure solid”.
Curiously, Russian Wikipedia tells a somewhat different story, stating that $...
5
votes
1answer
119 views
Help in understanding superconductivity?
I am a high school student doing a science project in superconductivity. My knowledge in physics is hence not pretty advanced but I am doing my best to understand the subject. What I find really ...
2
votes
2answers
196 views
Why does the bulk of a superconducting material expel magnetic field but not that of a perfect conductor?
It is well-known that when a superconductor (SC) is cooled below the transition temperature $T_c$, the magnetic field passing through the bulk of the SC is completely expelled. In Zee's book on ...
1
vote
0answers
30 views
Can an insulator become a conductor at superconductive temperatures?
Can an insulator become a conductor at superconductive temperatures? As a part of electric resistivity is physical opposition to the stream of particles would an insulator having its nuclei inert in ...
1
vote
1answer
31 views
Why the surface of the superconducting wire carrying current $I\ll I_C$ is where current mainly flow through instead of interior layer?
I am considering about a superconducting cylindrical wire carrying current $I\ll I_C$ ($I_C$ is the critical current). And based on 2nd London equation and Maxwell equation I arrived at the Laplacian ...
2
votes
1answer
255 views
Eddy current brake with superconductor
There are eddy current brakes used with metal plates to stop trains. It converts kinetic energy of the metal plate to heat via eddy current on it. So what if we have a superconducting metal plate and ...
4
votes
3answers
2k views
What's the reason for particle-hole symmetry operator to be anti-unitary?
I have been looking at some literature on Topological Superconductor, where the BdG Hamiltonian is frequently used, the $H_{BdG}$ has the so-called particle-hole symmetry, which is commonly defined ...
1
vote
2answers
158 views
A Question related to energy losses in superconductors
When we look at a superconductor, the conductivity is infinite. And when we apply a potential difference across the ends of the superconductor, the electrons have to start accelerating because there ...
0
votes
0answers
17 views
Do superinsulators violate the boundary condition of electric field?
In classical electrodynamics, static electric field is strictly curl free while magnetic field is strictly divergence free. As a result, the electric field component parallel to the surface and ...
3
votes
2answers
1k views
Interpolation formula for BCS superconducting gap
In BCS theory, the superconducting gap is given by solving at different temperatures the integral
$$\frac{1}{N(0)V}=\int_0^{\hbar\omega_c}\frac{\tanh\frac{1}{2}\beta(\xi^2+\Delta^2)^{1/2}}{(\xi^2+\...
1
vote
1answer
64 views
What does it mean to apply a voltage bias on a superconductor when $V = IR$ and $R = 0$ for a superconductor?
I have been reading papers about superconducting nanowire single photon detectors, and in them the voltage bias the superconductor to close to $T_c$ so that a photon has enough energy to break the ...