The study of physical properties condensed phases of matter, including solids and liquids.

learn more… | top users | synonyms

4
votes
2answers
718 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.
1
vote
1answer
145 views

How to derive the critical temperature for Bose-Einstein condensation of photon?

I found in Nature magazine that photon can have Bose-Einstein condensation. But I have a question how to derive the critical temperature for photon? Because the chemical potential of photon is zero ...
5
votes
1answer
97 views

Two-fluid description of superfluidity

I'm trying to teach myself about superfluidity and I'm slightly confused on the ''two-fluid'' description. From what I understand, the superfluid is considered to be a mixture of two fluids, a ...
3
votes
1answer
86 views

Phase Transition at Zero Temperature (Not QPT)

As is well known the Ising model exhibits a phase transition, except the one dimensional case in which the phase transition occurs strictly at $T=0$. Now I have always thought that this makes the case ...
1
vote
0answers
24 views

Why does the superconductivity hamiltonian have a µ term, while the superfluid does not?

In every discussion of SC and SF that I read (e.g. Simons), the SC Hamiltonian (BCS) has a $\epsilon_k - \mu$ in the kinetic part of the Hamiltonian, while the SF Hamiltonian has just a $\epsilon_k + ...
1
vote
1answer
45 views

Why spin-1/2 objects doesn't have quadrupolar magnetic moment?

I'm asking myself more generally why a spin of size S will feature multipolar states of degrees k up to 2S ? (This implies the question in the title : spin-1/2 can't have any quadrupolar ...
0
votes
0answers
15 views

What is the difference between finite displacement and linear response for calculating vibrational properties?

I see these concepts appearing in the context of calculating phonons and other vibrational properties, but I can't find a concrete explanation of the differences between linear response (DFPT) and the ...
4
votes
1answer
174 views

Why doesn't topological phase transition break any symmetry? Hidden symmetry?

This question may be superficial. However why all people saying this without a proof? Just like the "hidden variables" assumption in quantum mechanics, can one disproof that there is no hidden ...
5
votes
1answer
117 views

“Bosons are either gapped or condensated, except physical principle protected cases (Goldstone boson, photon).”?

Bosons are either gapped or condensated, except physical principle protected cases (Goldstone boson, photon, etc.). I read this in a paper (version1 of http://arxiv.org/abs/1404.3728v1, 1st page 1st ...
6
votes
1answer
122 views

Has anyone experimentally shown the quantized thermal hall conductivity in Quantum Hall systems?

For background: In a $D=2+1$ state with edge modes described by a chiral $( c_L \neq c_R )$ CFT there is a predicted thermal Hall conductance associated with the gravitational anomaly at the edge. ...
0
votes
1answer
36 views

Is time reversal symmetry broken in (conventional) superconductors?

How can one see it from BCS wavefunction and BCS Hamiltonian? i.e. $$H_{BCS}=\sum_{k\sigma}\epsilon_k c_{k\sigma}^\dagger c_{k\sigma}+\Delta\sum_k c_{k\uparrow}^\dagger ...
3
votes
1answer
71 views

Meaning of Time Reversal Symmetry

I was wondering if someone could give a simple explanation of what is meant by time reversal invariance. Is it analogous to spatial translational symmetry? If so, how? By spatial translational ...
1
vote
0answers
14 views

How does the Wigner-Eckart theorem rule Multipole Expansion?

I am wondering why a spin-S particle have only the term up to $k=2S$ in his multipole expansion ? It seems that the Wigner-Eckart theorem shows the relation between spin and multipole expansion but I ...
1
vote
1answer
38 views

why is DFT(Density Functional Theory) weak in evaluating semiconductor and insulator bandgaps?

we say that the DFT (Density Functional Theory) is to obtain the ground state properties of a quantum system and then we say: so, we can not use it to obtain the semiconductors and insulators band ...
2
votes
0answers
26 views

Isotope effect in BCS Theory

The BCS theory for supercondictivity says that the effect of variation of lattice ion mass (M) and its effect on transition temperature is given as $T_{c} \space\alpha\space M^{-\beta}$ . The ...
0
votes
1answer
50 views

At what densities the many-body approaches are valid?

Suppose we have a n-particle interacting system with a potential $V=a/(r1-r2)$, it is a pseudo-coulomb potential: you can choose it fermion or boson. Then, at what densities the many-body approaches ...
3
votes
0answers
39 views

How are resonating valence bond (RVB) states related to fractional quantum Hall (FQH) states?

In Kalmeyer and Laughlin's paper, there is an argument made for a frustrated two-dimensional Heisenberg antiferromagnet on a triangular lattice that if one uses a FQH wavefunction for bosons to ...
1
vote
2answers
47 views

How to verify/falsify the existence of localised edge states numerically?

I have to consider a Hamiltonian given in second quantized form in real space $$H = \sum c_k^\dagger h_{kl} c_l \, ,$$ describing fermions on a 2d hypercubic lattice. The concrete form of the matrix ...
1
vote
0answers
20 views

How geometry, and hence, a tight-binding Hamiltonian dictates the eigenvalues?

Considering an 'N' atom system, how should we understand the geometric dependence on the calculated eigenvalue spectrum by solving the nearest neighbor tight-binding Hamiltonian? A simple example ...
11
votes
1answer
356 views

Quasi 1D insulators with strong spin-orbital interaction

We know that the spin-1 chain realizes the Haldane phase which is an example of symmetry protected topological (SPT) phases (ie short-range entangled phases with symmetry). The Haldane phase is ...
1
vote
0answers
69 views

Anderson-Higgs mechanism for the (non-relativistic) $U(1)$ gauge theory under the unitarity gauge

On Page 138, Quantum Field Theory of Many-body Systems: From the Origin of Sound to an Origin of Light and Electrons by Xiaogang Wen, when he demonstrates the Anderson-Higgs mechanism for the $U(1)$ ...
1
vote
0answers
25 views

Does exciting an electron across the band gap change either its position or its localization?

I suspect that exciting an electron from its valence band to conduction band doesn't change its position, since the difference between the two bands are just their energies, but I want to know for ...
4
votes
1answer
193 views

Superconductivity in graphene with spin orbital coupling, is it proper to let the order parameter on two sub-lattice equal?

I am reading this article: Edge superconducting correlation in the attractive-U Kane-Mele-Hubbard model. Considering just the first part of the article, where a negative-U Hubbard model with the ...
0
votes
0answers
27 views

Topological term under electron-electron interaction

By integrating out fermions in gapped Dirac Hamiltonian, one can obtain a topological term for topological insulator. Why there is no further correction to this term when electron-electron interaction ...
1
vote
1answer
72 views

Atomic physics - lattice energy

Question: Why is ionic lattice energy inversely proportional to the radius of the atom? Most heterogeneous covalent molecules are polar to some extent. The degree of polarity, or the dipole moment, ...
2
votes
0answers
13 views

Random walk with self-transitions taking continuum limit

does anyone have any suggestions regarding how to correctly treat the continuum limit of a random walk that has non-zero self-transition probabilities? To put this concretely, let's say that the ...
0
votes
0answers
68 views

Macroscopic polarization operator (Berry's phase?)

I am faced with the problem of extracting the velocity from a density matrix which has a periodic nature with infinite spatial extent. This density matrix has time harmonic terms which hold the ...
3
votes
1answer
156 views

What's the difference between insulators and topological insulators?

What's the difference between insulators and topological insulators? When I asked some people about this, they told me that "because the topological insulators have gapless edge states,...", but what ...
5
votes
1answer
225 views

How to derive electron number equation of Bogoliubov Hamiltonian using thermodynamic relations.

My question arise from this article: Edge superconducting correlation in the attractive-U Kane-Mele-Hubbard model. I will describe my question in detail so that you might not need to look into that ...
0
votes
0answers
49 views

On the Bogoliubov transformation in the BCS

I have a question regarding the diagonalization of the BCS-Hamiltonian using the Bogoliubov-DeGennes-transformation. I hope someone can help me, so I start with the following Hamiltonian, it is ...
8
votes
2answers
347 views

Precise statement of Mermin–Wagner theorem

Roughly speaking, Mermin-Wagner theorem states that continuous symmetries cannot be spontaneously broken at finite temperature in systems with sufficiently short-range interactions in dimensions ...
1
vote
0answers
38 views

Argument of E. Fradkin on the mean-field theory of spin liquids

I have read the chapter 8 of Field Theory of Condensed Matter Physics (2ed.) by E. Fradkin a couple of times, but I still confused by his argument at some points. I hope you can help me with that. ...
2
votes
1answer
216 views

Does the low-energy gauge structure depend on the choice of $SU(2)$ gauge freedom?

The starting point and notations used here are presented in Two puzzles on the Projective Symmetry Group(PSG)?. As we know, Invariant Gauge Group(IGG) is a normal subgroup of Projective Symmetry ...
2
votes
0answers
47 views

Writing a Green function for Tight binding Hamiltonian?

Tight binding Hamiltonian can be written as $H=-t\sum_ic_ic^\dagger _{i+1}+h.c$ where as green function for a system can be written as $G^{-1}=iw-H$ From above Hamiltonian you can see that we can ...
1
vote
1answer
119 views

Point group symmetries and unit cell

I was wondering if the unit cell (of a given lattice) had to have every point group symmetries of the lattice it defines ? I guess there is no unique way to define a unit cell and that it may not have ...
0
votes
1answer
127 views

Does graphene have a honeycomb lattice?

In my grand ignorance I would state that graphene has a honeycomb lattice. Some tend to agree with me and some others do not. I'm curious to know what members of the SE community think is the right ...
1
vote
1answer
90 views

How to obtain the asymptotic behavior of Green's function?

This question arose from Eq.(9.135) and Eq.(9.136) in Fradkin's Field theories of condensed matter physics (2nd Ed.). The author mapped quantum-dimer models to an action of monopole gas in $(2+1)$ ...
3
votes
2answers
109 views

Rigorous distinction between quasiparticles and collective excitations

I would like to hear your opinion on the question whether there is an accepted distinction between both concepts in condensed matter physics. I would tend to use the word quasiparticle for dressed ...
4
votes
2answers
77 views

Destroying currents in superconducting rings by vortex tunneling

Consider a superconducting metal ring in which there is a persisting current $I$. I am interested in the failure of this current to remain "persisting" in the ring, although this will occur at ...
1
vote
0answers
21 views

How to expand free energy of Heisenberg spin chain?

In Dasgupta & Ma's 1979 paper "Low-temperature properties of the random Heisenberg antiferromagnetic chain", they give the free energy of a few interacting Heisenberg spins on a chain. I can't ...
20
votes
4answers
871 views

What observables are indicative of BCS Cooper pair condensation?

What observables are indicative of BCS Cooper pair condensation? "Thought" experiments and "numerical" experiments are allowed. This question is motivated by the question Has BCS Cooper pair ...
2
votes
0answers
126 views

Questions on the elementary excitations in the resonating-valence-bond(RVB) states?

It is known that the RVB states can support spin-charge separations and its elementary excitations are spinons and holons. But it seems that there are some different possibilities for the nature of ...
3
votes
3answers
93 views

Fourier Transforms Related to Green's Functions

I'm reading a text on field theory where there are a number of assertions made about Fourier transforms that I'm finding confusing. For example, let $G^R = -i \theta(t - t')e^{-i \omega_0 (t - t')}$. ...
1
vote
0answers
83 views

Precisely speaking, does photon become massive or the phonon become massive, due to Higgs mechanism in superconductor?

Consider the low-energy field theories of superfluids and superconductors. In superfluids, the spontaneous breaking of the order parameter's phase creates phonons as the massless Goldstone ...
8
votes
1answer
789 views

Kramers-Kronig relations for the electron Self-Energy Σ

I'm currently studying an article by Maslov, in particular the first section about higher corrections to Fermi-liquid behavior of interacting electron systems. Unfortunately, I've hit a snag when ...
1
vote
2answers
364 views

Momentum change in collisions (Drude model)

A particle suffers elastic collisions with scattering centers with a probability of collision per unit time $\lambda$. After a collision the particle is in a direction caracterized by a solid angle ...
3
votes
1answer
64 views

How the Vortex containing majorana bound state is non-abelian statistics

Recently,I read some papers about non-abelian statistics of majorana fermion, such as: Majorana Returns F. Wilczek http://www.nature.com/nphys/journal/v5/n9/full/nphys1380.html and Non-Abelian ...
5
votes
1answer
120 views

Topology of Fermi surface

In The universe in a Helium droplet, Grigory Volovik relates the stability of a fermi surface to topology of a Green function. There he gives the example of a Fermi gas and says that the Green ...
1
vote
2answers
94 views

Why does the “counting rule” of band theory fail to predict the conduction properties of some materials?

I'm a little confused by the description I commonly hear about the electron counting rule in band theory. The general statement I find is that a "solid with an odd number of electrons per unit cell ...
1
vote
0answers
33 views

Winding number for SSH model

The Hamiltonian for SSH model can be written as $h(k)=\begin {pmatrix}0&t_1+t_2exp^{-ika}\\t_1+t_2 exp^{ika}&0 \end{pmatrix}$ for finding the topological invariant Why we only calculate the ...