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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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18 views

Energy Stored In Superconductor

I have two questions regarding this topic: What is the equation to calculate the energy stored in a superconductor when you apply a current. I’ve been looking it up and have been getting ...
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Schrieffer-Wolff Transformation for conventional superconductors

I was trying to follow the discussion in Radi A. Jishi's book (Feynman Diagrams in Condensed Matter Physics), Chapter 12 on superconductors. They basically have a Hamiltonian that comprises of a ...
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Why is the Mermin Wanger theorem not considered for superconductors in 2D?

Several papers set up a model of fermions in 2D and calculate superconducting $T_c$, e.g.: https://arxiv.org/pdf/1808.08635.pdf https://arxiv.org/pdf/1406.1193.pdf https://www.pnas.org/content/pnas/...
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Why isn't too restrictive to consider a connection of the form $-iA$ in the magnetic Ginzburg-Landau model?

I'm facing this equation as a mathematician, so the problem could easily be my lack of knowledge in physics. In the magnetic Ginzburg-Landau model the energy has the form $$ E(A,\phi)=\int_{\mathbb{R}...
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What do I need to study to develop a room temperature superconductor? [closed]

The title says it all. I'm 18 and I'm an electrical engineering major, I want to develop a room temperature superconductor.
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How and why Liquid helium climbs the walls of the container it is kept in?

Liquid helium (He-II) shows a strange phenomenon, where it flows on its own, forming films across the surfaces of the container it is kept in. How and why this happens and how is it possible?
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What is the physical meaning of the particle-hole symmetry in condensed matter physics?

It is often mentioned that a mean-field BdG Hamiltonian for a superconductor has the particle-hole symmetry. i.e., if $|\Psi_{\mathbf{k}}\rangle$ is an eigenstate of $H^{BdG}_{\mathbf{k}}$ with ...
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Why is phason/amplitudon in CDW parity odd/even?

The question is about collective modes of charge density waves, i.e., amplitude and phase fluctuations $\delta,\phi$ of the order parameter $\Delta(x,t)=(\Delta_0+\delta)e^{i\phi}$. I read in many ...
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Do surface currents in superconductors only arise due to an externally applied magnetic field?

On the topic of surface currents or (screening currents) which are responsible for non decaying eddy currents that expel an externally applied magnetic field, does this phenomenon only occur when ...
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Where does the superconducting density of states come from?

I'm going through Tinkham (2nd edition) and in section 3.7.1 he makes a claim which seems quite weird: $N_n(\xi)$ is the Normal density of states (normal mode), so how would it be that the density of ...
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Electron and holes in tight binding Hamiltonian on two sublattices

Background Say that I have a tight binding Hamiltonian (with spinless fermions) of the form $$H = - 2t \sum_{ij} (c_i^{\dagger} c_j + h.c) - 2\mu \sum_i c^{\dagger}_i c_i$$ where we only sum over ...
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What causes current to move to the surface in superconductors?

I’m really trying to understand superconductors in an intuitive way here, although many say you cannot, anyway Im unable to find anywhere that explains to me why the current is on or near the surface ...
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In superconductors, is the Meissner effect a result of the surface currents?

Basically I’m trying to understand whether the current moving to the surface of the conductor is a cause or an effect of the Meissner effect. If it’s a cause, then what phenomena causes the current to ...
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What causes expulsion of magnetic fields in superconductors specifically?

The only thing I’ve been able to find about this is that in superconductivity, you get surface currents the exactly cancel the field that would otherwise penetrate, and yes I know sometimes it ...
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The magnetic flux in a superconductor (zero resistance) spire never changes?

I was reading a book and the author said that the magnetic flux never changes when a spire has resistance 0. I am sort of confused by this, can somebody explain me better?
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What is Fermi Surface of superconductors?

It is known that, in superconductors, at the Fermi level, electrons are paired(Cooper pairs) and there is a gap (see figure). However, there are lots of ARPES experiments showing the "Fermi surface" ...
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Induction to remove current from superconductor?

I’ve read how you can insert current into a superconductor. I was wondering if you could use a similar method of induction to remove current from the superconductor for use.
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Why do tokamaks have so few toroidal field magnets?

From the ITER webpage itself, the tokamak has only eighteen toroidal field magnets. If the magnetic field is directly and linearly dependant on the number of coils around the torus, then why did the ...
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Critical Current Density vs Critical Current

What is the difference between critical current (Ic) and critical current density (Jc)? How do they relate to one-another?
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Achieve geosynchronous orbital speeds at leo while moving relative to a electric field

Would it be possible for an object to move at geosynchronous orbital speeds at LEO? Assume that a superconductive ring extending around the entire Earth existed at the same height as the ISS. Could an ...
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1answer
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Why is average magnetisation zero in a normal (Non-superconducting) state

Considering type-I superconductors (specifically the magnetisation curves), why can one assume that the magnetisation is zero when we consider a normal state (when $H>H_C$)? EDIT: For ...
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What is a rigid wave function?

The London equations prior to BCS that describe superconductivity require assuming the wavefunction describing the superconducting pair of electrons to be rigid. I've been looking all over trying to ...
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Predicting the superconductor critical temperature

I am fairly new to superconductors, but am attempting to understand BCS theory. Is BCS Theory, or any other tested theories of superconductivity currently capable of predicting the transition ...
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Questions about unitary condensate wave-function and $p_x+ip_y$ superconductor

I read about the unitary and non-unitary order parameter states here https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.75.657 and https://arxiv.org/abs/1512.01151 The form of the order ...
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Covalent bonding in cuprates

In high temperature cuprate superconductors like YBCO, there are intermediate copper-oxide planes, where $Cu$ and $O$ atoms are arranged alternatively in a square lattice. In this arrangement, the $Cu$...
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What is the minimum area of a superconducting disk needed to flux pin against the Earth?

I'm imagining a massive ultra thin disk of YBCo or some other high temperature conductor that is surrounded by a layer of liquid nitrogen or other coolant and insulated by a layer of aerogel or other ...
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Superconducting Gap in Superconductors

Please explain "Exponential behavior usually signals the presence of a gap in the energy spectrum" How The presence of a gap explains the exponential decrease of the specific heat and the thermal ...
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Electric field outside superconducting wire

I understand that in a superconducting wire you have no electric field and no magnetic field(or at least these enter by a small amount given by the London penetration depth) and the current resides ...
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It is possible that without resistance current flow a conductor [closed]

It is possible that without resistance current flow a conductor (answer with proof by)
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Experimental lower bound on the lifetime of a supercurrent?

Nothing is perfect, everything has friction---except in quantum physics, where macroscopic superconductors allow for dissipationless currents. It's an astounding theoretical prediction, and so it is ...
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Superconductivity as a macroscopic phenomena

I have been doing some reading on the formulation of BCS superconductivity. From what I understand, an additional non-vanishing term $\Delta c_{\uparrow,k}c_{\downarrow,-k} + c.c$ develops below the ...
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Particle Hole symmetry in Interacting superconductor

For noninteracting superconductors (fermion hopping plus fermion pairing), there is a particle hole (PH) symmetry which is a redundancy. The redundancy says that the BdG Hamiltonian satisfies the ...
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Why do magnetic field lines wrap around the other side of a super diamagnet instead of redirecting completely away?

Super conductors are perfectly diamagnetic in that they perfectly expel a magnetic field. To me that means that if the source of a magnetic field is on one side of a super conductor, the other side ...
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Diamagnetic current in the BdG superconductor

Recently, I am following the paper arXiv:1610.01803 to study superfluid weight. In this paper the diamagnetic current is given by: $j^D_{\mu}(\vec{q})=\sum_{\vec{k},\sigma}\partial_{\mu}\partial_{\...
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Laminar structure

I am currently reading 'Introduction to Superconductivity' by Michael Tinkham. In the second chapter (introduction to electrodynamics of superconductors) Tinkham goes on to describe the idea of the ...
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BCS theory and Cooper pairs

I'm studying superconductivity and BCS theory. Looking at the BCS ground state construction, I see two things that seem conflicting Occupation of Cooper pairs in BCS ground state (look at the figure ...
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3answers
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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 ...
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1answer
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Dimagnetism proof for superconductivity

I came across an article that dimagnetism is one of the proof so that a material can act as superconductor. So what is dimagnetism.
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What is the effect of the global $U(1)$ spontaneous symmetry breaking on the physical observables in superconductors?

I have been taught that in Ginzburg-Landau model for superconductors the transition to the superconductive states lead to the spontaneous symmetry breaking of global $U(1)$ symmetry. While I have ...
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Is there a theoretical ground for ionic superconductivity?

I've been wondering for a while if there's a possible theoretical ground for ionic superconductivity, or whether it is at all possible from a thermodynamic and condensed matter physics standpoint. ...
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Wavefunction of Cooper Pairs

I tried to solve the wave-function of cooper pairs but i am stuck in an integral equation and have no idea how to solve for the wave-function. Before, i tell you how i got the integral in brief. ...
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1answer
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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 ...
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Can you lock multiple magnets to a single superconducting puck?

We've all seen the videos of a superconducting puck floating above a track of magnets. Could another magnet be locked above the puck? I ask this with the intention of attaching vacuum insulator to the ...
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flux threading through superconducting ring

I have been confused over the wording used in this paper describing RSFQ logic circuits: http://www.mukhanov.com/uploads/LikharevSemenov-RSFQReview_IEEETAS91.pdf From page 6: " If such a single flux ...
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Position of coherence peaks in linear density of states for d-wave and extended s-wave symmetry

Where do the coherence peak singularities in the linear density of states lie for d-wave and extended s-wave pairing symmetries? In particular, what is the value of the gap between the coherence peaks ...
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Eigenvectors of the BCS Hamiltonian

In introductory superconductivity one often studies the BCS Hamiltonian $$H= \begin{pmatrix} \xi & -\Delta \\ -\Delta & -\xi \end{pmatrix} $$ I can find the Eigenvalues and Eigenvectors by ...
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Spin rotation symmetry in triplet superconductors

Triplet superconductors can be described using the $d$ vector formalism and many properties of the superconducting states can be checked via operations on the $d$ vector itself. I want to know how can ...
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Why is mercury a type I superconductor and Niobium is a type II superconductor? What makes them two different types of superconductor?

What structural and physical differences are there that separates Nb and Pb into two different type of superconductor?
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How does Cooper pair move in a lattice according to BCS

According to BCS theory, the cooper pairs have opposite momenta, but according to this animation http://www.superconductors.org/bcs_anim.GIF the electrons in the pair seem to move in the same ...
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Characteristic lengths in SNS Josephson Junction

An S-N-S Josephson junction is formed by two Superconducting (S) leads separated by a normal metal (N) which acts like the weak link. While studying, I often encounter the words diffusive, long, ...