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

learn more… | top users | synonyms

2
votes
0answers
36 views

Why does Pressure Increase the Tc (Critical Temperature) of a Superconductor?

Just a heads up - please make this answer understandable to around 1st year degree level physics - not PhD research. So I can understand it - thanks. I was wondering why they Critical Temperature ...
1
vote
1answer
63 views

Why isn't doped silicon a strongly correlated electron system?

Most books on strongly correlated electrons claim that when the number of itinerant electrons is small and the screening length is large, that the system becomes "strongly correlated", (i.e. the ...
6
votes
1answer
141 views

Real part of the AC conductivity has a discrete spectrum => What physics?

If the real part of the AC conductivity $\text{Re}[\sigma(\omega)]$ has a discrete spectrum only, i.e., $\text{Re}[\sigma(\omega)]=a_1\delta(\omega-\omega_1)+a_2\delta(\omega-\omega_2)+\cdots,$ what ...
2
votes
4answers
398 views

Bogoliubov transformation with a slight twist

Given a Hamiltonian of the form $H=\sum_k \begin{pmatrix}a_k^\dagger & b_k^\dagger \end{pmatrix} \begin{pmatrix}\omega_0 & \Omega f_k \\ \Omega f_k^* & \omega_0\end{pmatrix} ...
6
votes
1answer
113 views

How legit is this paper claiming to have observed Hawking radiation? [closed]

I recently stumbled upon this paper. In it, the author claims to have found a signature for Hawking radiation in a condensed matter system. I know that experimentalists have been trying to find ...
2
votes
1answer
84 views

How to distinguish between a topological state from from a non-topological one?

How to distinguish between a topological state from from a non-topological one? Is there any standard procedure for identifying the topological features of a given hamiltonian? In general what are the ...
2
votes
0answers
59 views

Is many-body Hamiltonian valid in strong-correlated system

Condensed-matter textbook often states that there is a many-body Hamiltonian $$ H= \sum_i \frac{ p_i^2}{2m_i} + \sum_{i>j} V_{ij} \tag{1} $$ where $V_{ij} = Z_i Z_j/r_{ij}$. This Hamiltonian ...
0
votes
0answers
38 views

Hartree Fock exchange kernel

I would like to understand, how we calculate the exchange kernel of the Hartree Fock equations for a coulomb potential. So in slide 19 here for example you see the result, but I have not the ...
0
votes
0answers
28 views

How does quantum confinement happen in amorphous or polycrystalline materials?

You can easily find papers where they make a nanostructure (thin film, nanowire, or quantum dot) from methods (ALD, CVD, thermal/egun evaporation) that produce amorphous or polycrystalline structures ...
3
votes
0answers
113 views

Symmetry, gauge, and projective symmetry group (PSG)?

My following questions come from the understanding of the relations between the PSGs for two gauge-equivalent mean-field (MF) Hamiltonians (or MF ansatz). Considering the Schwinger-fermion ...
6
votes
3answers
210 views

Hollow gold bar

A scammer got a hollow gold bar and fills it with a combination of lead and air, with the same average density as gold. What's the simplest way of discovering the fraud? I know that x-rays will see ...
3
votes
0answers
76 views

Non-abelian bosonization

Reading this review about non-abelian bosonization, Non-abelian bosonization by I.Karmazin, I stumbled about two questions Below equation 6, I don't get the final point in the statement about the ...
6
votes
1answer
444 views

How can one localize the massless fermions in Dirac materials?

I noticed that finite electric potential cannot localize the low energy excitations in a graphene sheet. Is it possible to localize the massless fermions in the surface band of topological insulators ...
0
votes
1answer
62 views

A problem about solving energy bands by the method of second quantization

In hopping model, we can get the Hamitonian as $H_0=-t\sum a^\dagger_ia_{i'}$. Then we take the fourier transform and put the operator which are in momentum space in the Hamitonian above. However, I ...
3
votes
0answers
78 views

How to generalize BdG equation in order to match a graphene with a metal superconductor?

I want to generalize BdG equation in order to compute the conductance of a junction of graphene with a metal superconductor. The previous works done until now on this hetrojunction is devotted to use ...
3
votes
0answers
55 views

Tunneling from Dirac material into Schrodinger material?

When a Dirac material, like graphene or TI, has a connection with a normal metal which Schrodinger equation govern on their carriers, how could we manipulate the tunneling of electron from Dirac side ...
6
votes
1answer
181 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 ...
1
vote
0answers
26 views

Why isn't there a different phase after fourier transformation in two lattices

I am trying to understand some solutions for graphenes energy dispersion. While most of it is clear, I don't get one step, when changing into k-space. Consindering two sublattices A and B with ...
2
votes
0answers
76 views

Time reversal operator in tight-binding model with second quantization form

In tight binding model, $H=\sum_{r,r'}ta^{\dagger}_{r}a_{r'}+h.c.$.When now conducting a time reversal transformation, what form will this Hamiltonian like? Or how can I express time reversal ...
0
votes
1answer
38 views

Negative pressure experiments

One method of understanding the physics of materials is to study their properties under the effect of pressure. Under high pressure, new phases can arise. Experimentally, high pressure can be obtained ...
6
votes
2answers
439 views

Symmetry Breaking And Phase transition

Is every phase transition associated with a symmetry breaking? If yes, what is the symmetry that a gaseous phase have but the liquid phase does not? What is the extra symmetry that normal $\bf He$ ...
5
votes
2answers
1k 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 ...
1
vote
0answers
109 views

Deriving Graphene energy dispersion in tight binding model

I'm trying to get into graphene, in detail, I try to derive the elec. energy dispersion. Sadly, I am not that familiar with condensed matter QM by now, so I got some basic questions and I hope to find ...
8
votes
3answers
739 views

Is there a connection between the fluctuation-dissipation theorem and the Green–Kubo relations?

Is there a connection between the fluctuation-dissipation theorem and the Green–Kubo relations? I have a hard time finding out if there is a relation and what it is, because the ...
1
vote
0answers
72 views

Simple questions on the symmetric eigenstate and time-reversal (TR) breaking eigenstate?

Followings are two independent questions as implied by the title: (1) Considering a quantum Hamiltonian $H$ possesses some symmetries described by a symmetry group $G=\left \{ g_1,g_2,...,g_n \right ...
1
vote
0answers
35 views

Conductivity Matrix (Symmetry Information)

I'm trying to understand the symmetry content of the conductivity matrix: one information is, presence of time-reversal symmetry causes the off-diagonal terms to vanish. When this is broken (e.g. in ...
2
votes
0answers
40 views

Discrete Symmetries: Breaking and Preserving

This is not a question, let's list down all the effects resulting from breaking or preserving of various discrete symmetries, on various observables, be it in condensed matter or in high energy. ...
20
votes
4answers
852 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 ...
4
votes
2answers
177 views

Why are most ferromagnets metals while antiferromagnets are insulators?

This seems to be experimentally true, but I don't quite have an intuition as to why. In the Ising model, we usually consider an insulating ferromagnet if $J>0$, where $J$ is the exchange coupling. ...
3
votes
1answer
83 views

How to see the ground state degeneracy (GSD) from a $BF$ theory in $2+1$ $d$?

I have seen many times the $BF$ theory has non-trivial ground state degeneracy (typically on torus), but I can not see how the conclusion come out. Recently I found a paper by Hansson, Oganesyan and ...
1
vote
0answers
232 views

The reciprocal lattice of HCP lattice

There is a very similar question here Reciprocal Lattice of a non-bravais lattice, but I don't fully understand the answer, and the question is now obsolete so I feel that I should ask it again. How ...
2
votes
0answers
89 views

Pedagogical introduction to vertex, domain wall, and kink

Recently, Majorana fermion becomes hot in condensed matter physics. The concepts: vertex, domain wall, and kink often appear in these articles about Majorana fermion. I have no idea about the ...
4
votes
2answers
587 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.
0
votes
0answers
17 views

Applicability of Fano resonance

I know that Fano resonance$^{1,2}$ can be applied for the interaction between a discrete excited state, $|\phi_0\rangle$, and a continuum of excited states, $|\phi_E\rangle$. These are related to ...
19
votes
2answers
2k views
0
votes
0answers
80 views

Time evolution operator of a periodic Hamiltonian

Suppose we have a Hamiltonian $H(t)$ with periodicity $T$. The time evolution operator in a full period is $$U_1=\cal{T}e^{-i\int_0^T H(t)\mathrm{d}t}$$, where $\cal{T}$ is time ordering operator; ...
2
votes
0answers
41 views

Hartree-Fock MFT & Large-N MFT

My question may be similar to the one in this post, but the motivation for me to raise this one is that, in strongly correlated systems, physicists sometimes seem to prefer the "large-$N$" MFT to the ...
5
votes
1answer
342 views

What is the difference between spin glass and spin liquid?

What is the difference between spin glass and spin liquid? Do they both originate from frustration?
6
votes
2answers
480 views

Definition of short range entanglement

When studying Symmetry Protected Topological phases, one needs to define what a short range entangled (SRE) states means. But there appears to be different definitions that are not equivalent to each ...
2
votes
0answers
50 views

Detailed Balance for Quantum Master Equations from System Hamiltonians with Degenerate Spectrum

Kossakowski, Andrzej, et al. ("Quantum detailed balance and KMS condition." Communications in Mathematical Physics 57.2 (1977): 97-110) gave a proof that the stationary state of a quantum dynamical ...
4
votes
1answer
955 views

Looking for a complete review of the BEC-BCS crossover

I'm looking for comprehensive review of the BEC-BCS crossover, both from a theoretical point of view, and from a experimental one. Even something at textbook level, but exhaustive, would be OK, but I ...
3
votes
2answers
3k views

Physical meaning of magnetic length

What is the physical meaning of magnetic length $\ell_B=\frac{\hbar c}{e B}$ in 2D electron system under magnetic field? When $\ell_B \longrightarrow a$, where $a$ is the lattice constant, does that ...
1
vote
3answers
134 views

How to get conductivity from Green function $\mathcal{G}(x_1,x_2,\tau)$ of inhomogeneous system?

I'd like to study an inhomogeneous system, i.e., momentum is not a good quantum number therein. Therefore, I tried to calculate temperature Green functions like $\mathcal{G}(x_1,x_2;\tau)$, or its ...
0
votes
0answers
14 views

Bounding the energy gap of a local spin Hamiltonian

What are some common mathematical techniques for bounding the gap between the ground state and first excited state of a local spin Hamiltonian? Does anyone have any good references for this?
1
vote
0answers
28 views

Mean-field approach to quantum phase transitions in Fermi systems

I have a basic confusion concerning the mean-field theory of quantum phase transitions in Fermi systems. Consider as an example the BCS theory of superconductivity in a Dirac fermion system, ...
0
votes
0answers
17 views

dynamic structure factor for nucleation

I know that using the peak position/moment of structure factor or may be by first zero or minimum of pair correlation function we can estimate the characteristic length scale in a phase separating ...
0
votes
0answers
33 views

pair correlation function for heterogeneous nuclei

I have a system with heterogeneous size of nuclei of two liquids within a mixed fluid phase of those two liquids. I was wondering what would be the interpretation of pair correlation function for a ...
3
votes
2answers
98 views

Are critical exponents below and above the critical point always same?

The scaling relations don't distinguish the the critical exponents below and above the critical value. In the mean field level, I understand these critical exponents are same whatever one approaches ...
5
votes
2answers
675 views

Why can, or can not, a perfectly incompressible fluid exist?

Water is normally assumed to be an incompressible fluid - for example in the context of calculations involving water pressure. I wondered whether that is strictly true, or an approximation? Later I ...
61
votes
5answers
6k views

What challenges needed to be overcome to create (blue) LEDs?

In light of today's announcement of the 2014 Nobel laureates, and because of a discussion among colleagues about the physical significance of these devices, let me ask: What is the physical ...