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

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132 views

Free electron gas in two dimensions

Can someone give a qualitative description on why the density of states for a two dimensional free electron gas is independent of energy while it is not in one and three dimensions? In one dimension ...
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0answers
67 views

Approximation of skeleton diagrams

I'm studying the diagrammatics for a Bose system (in the superfluid phase) developed by Gavoret and Nozieres (Annals of Physics 28 349 (1964)). In this paper, they show how to solve the problem using ...
2
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1answer
79 views

Out-of-Plane Phonons

I am trying to derive the out-of-plane phonon dispersion relation for a membrane. As far as I can tell, one of the simplest ways to do so is with a Lagrangian of the form: ...
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176 views
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117 views

Pseudocubic unit cells: how to construct one?

I keep coming across the term pseudocubic unit cell while reading about orthorhombic perovskite structures. No clear explanation ...
9
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1answer
462 views

How to determine if an emergent gauge theory is deconfined or not?

2+1D lattice gauge theory can emerge in a spin system through fractionalization. Usually if the gauge structure is broken down to $\mathbb{Z}_N$, it is believed that the fractionalized spinons are ...
8
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1answer
421 views

Nambu-Goldstone bosons from a quantum anomaly symmetry breaking?

We know that: Nambu-Goldstone bosons come from Goldstone theorem: a spontaneous (continuous)-symmetry breaking of the system leads to massless scalar modes. quantum anomaly: is the anomalous ...
4
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1answer
531 views

What is an electron/hole pocket and what is the significance?

What is an electron/hole pocket and what is the significance? I'm trying to get my head around this. I've read what Ashcroft and Mermin have to say on the subject, but it's a little convoluted. They ...
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1answer
194 views

What does (001) Silicon mean?

If someone gives me a thin film of Si, and they tell me it's (001) Si, does that mean that the (001) planes of Si are the ones making up the surface of the film?
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100 views

Symmetry argument about degeneracy of graphene energy band at Dirac point

This question is very related to the thread here. In the answer given by @BebopButUnsteady , the statement is that as long as the inversion and time-reversal symmetry are respected, the Dirac points ...
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2answers
175 views

How to conclude that an interaction is attractive from its Fourier transform (momentum space representation)?

Background: In the book by Altland and Simons, Condensed matter field theory, in exercise 4.5.7, one is supposed to use the effective field theory method to integrate out the phonon field in an ...
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2answers
84 views

Is this two forms of Hubbard model equivalent?

I have seen two form of Hubbard model, one is: $$H=-t\sum_{<ij>s}c_{is}^\dagger c_{js}+h.c.+U\sum_i(n_{i\uparrow}-1/2)(n_{i\downarrow}-1/2)-\mu\sum_{is}n_{is}$$ The other is a more familiar ...
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77 views

1+1D Bosonization on a line segment or a compact ring

I have been informed that 1+1D Bosonization/Fermionization on a line segment or 1+1D Bosonization/Fermionization a compact ring are different - Although I know that Bosonization can rewrite fermions ...
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69 views

Why p-wave superconductors are rare in nature?

I have the basic question that why so many superconducting materials are s-wave and d-wave pairing, but the p-wave superconductors are so rare in nature? An equivalent question may be that why ...
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99 views

How should I regularize this integral?

I need to calculate the following integral (which is divergent): \begin{equation} I(m,C)=\int_{-\infty}^\infty {\rm d}\omega\int_{\rm space}{\rm d^3 ...
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0answers
40 views

How Does The Macroscopic Wavefunction Build Up?

How does the macroscopic wavefunction (the order parameter) builds up from zero value to the a finite value when liquid He undergoes a transition from normal to the superfluid state? How does it ...
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0answers
71 views

The temperature dependence of the electron-hole (or particle-hole) continuum

In the theory of the electron gas, the particle-hole pairs are possible elementary excitations. I would like to know how the temperature T affects the particle-hole continuum which defines the domain ...
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61 views

band gaps in tight binding model

What happens at the zone boundaries of the brillouin zones in the tight binding model? How does the band gap originate in the TB model?
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1answer
176 views

How to obtain band dispersion from a band structure diagram?

Reading about bands dispersion, I came across the following (Computational Chemsitry of Solid State Materials): ...
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0answers
82 views

Debye Hückel Theory valid for ions?

I am wondering about the following: Is Debye Hückel Theory only used if you look at how an external "strong" field(like a potential by a sphere that has a charge that is 1000times higher than the ...
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1answer
183 views

Why does a bucket of Water weigh more than a bucket of Air?

Given the numerous chemical compounds found in dry air [compressed into a liquid] of a given volume [lets say $22.4$ L for simplicities sake] whose atomic weights far surpass that of water alone ...
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0answers
163 views

What is the meaning of inflection points in the dispersion relation inside the first Brillouin zone?

I have a question regarding the $E$ vs $k$ curve in the first Brillouin zone. Why does the curve have an inflection point at some value of $k$ in the curve? How does it physically support it?
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2answers
602 views

Is there a sound theoretical argument against inner-shell induced nuclear chain reactions?

There is a claim often made about cold fusion, that it is excluded theoretically. The main theoretical argument is that electronic energies are too low to overcome the Coulomb barrier, since d-d ...
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0answers
48 views

A small contradiction between periodic boundary condition and first Brilliouin zone

In condensed matter, one usually considers Bloch states inside the first Brilliouin zone, which, for 1d system with lattice constant $a$, is $-\pi/a<k<\pi/a$. But the basis of this, Bloch ...
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124 views

Good introduction to many-body Green's function via path integral formulation?

Can anyone kindly provide any information on valuable references or books on this topic? It appears to be prevalent in 90s papers on High-Tc superconductivity or quantum Hall effect, especially in a ...
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1answer
361 views

Band gaps: are they at the centre or at the edge of the Brillouin zone?

Reading about electronic band structures, I came across the following: Band gaps open at the edges of the Brillouin zone (BZ), since that is where the Bragg scattering occurs. I am slightly ...
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95 views

Variational principle

In the LMTO method, the interstitial region is approximated by plane waves and the muffin tin region of the potential by solutions to the radial Schrodinger equation. In using the variational method ...
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49 views

Introduction and overview of Condensed Matter Physics [duplicate]

Is there any book that provides an overview of Condensed Matter Physics? I have had a course in QM and statistical physics and some. I dont know anything about this field, so is there a readable ...
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675 views

Numerical problem in solving the Bogoliubov de Gennes equations- methods to solve?

I am trying to solve an assignment on solving the Bogoliubov de Gennes equations self-consistently in Matlab. BdG equations in 1-Dimension are as follows:- $$\left(\begin{array}{cc} ...
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36 views

Quantum Hall Effect Dark Matter Detector?

Has anyone used a Quantum Hall effect detector to detect dark matter? I was looking at the following animation on wikipedia: ...
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28 views

Can the short-time dynamics of an open quantum system be approximately unitary?

Considering the physics of an open quantum system described by a Hamiltonian $H=H_S+H_E+H_{SE}$, where the subscript $S$ refers to the system of interest, $E$ to the environment and $SE$ to the ...
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70 views

Does the Fermi sea have plane waves, or wave packets?

Consider a zero-temperature, one-dimensional crystal with allowed electron momenta $k_n = \frac{2\pi n}{L}$. Question: Which is the more correct way to think about the Fermi sea? Sharp plane ...
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1answer
166 views

Significance of magnetic translation operator defined in fractional QHE's description

What is the significance of the magnetic translation operator used in describing the Fractional Quantum hall effect? I was following Anthony Leggett's lecture video in which he defines these operators ...
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0answers
21 views

Is there a way to quantify how similar a polycrystal should behave to a single crystal?

So in solid state classes we learned about phenomena like band structure and others arising from a periodic potential. Then we get to doing actual experiment and find out that materials being single ...
4
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1answer
140 views

String-net models on non-trivalent lattices

I have just started reading about string net models. The following aspect wasn't entirely clear to me: String net models are most naturally defined on trivalent networks, that is to say networks ...
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187 views

Why is there a Majorana zero mode in the $\pi$ flux core of the p+ip superconductor?

In this review paper (http://arxiv.org/pdf/1202.1293.pdf), the author shows that threading a $\pi$ flux through a 2D $p_x+ip_y$ superconductor will trap a Majorana zero mode at the flux center. The ...
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256 views

Is non-relativistic quantum field theory equivalent with quantum mechanics?

Related post Can we "trivialize" the equivalence between canonical quantization of fields and second quantization of particles? Some books of many-body physics, e.g. A.L.Fetter and ...
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0answers
50 views

Fractional quantum number induced in a soliton profile

It has been known there is fractional quantum number induced in a soliton profile, such as this Jeffrey Goldstone and Frank Wilczek paper and many works of Jackiw. For example the electric charge ...
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2answers
1k views

Dispersion Relation (e vs. k) clarification (crystal momentum or electron momentum)

If we get the dispersion relation from the Fourier transform of the lattice vectors then how do we get electrons information? Specifically, for the $k=0$ point of the graph, does this mean the ...
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0answers
82 views

about orthogonal catastrophe

I am reading Wen's book, QFT of many-body systems ( @Xiao-Gang Wen ). I am a little confused about the orthogonal catastrophe introduced in Chap.5. Below Eq.(5.1.6), it is stated that ``the influence ...
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3answers
212 views

Why are free electrons free?

This is what I understand so far: in a conductor, the ions have a weak pull on the valence electrons. So when an electric field is applied, the free electrons are able to easily move about. Makes ...
5
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1answer
269 views

Topology and Majorana bound states

I'm working at the moment on Majorana Bound states and their topological properties. Now I have a question about it. The Altland-Zirnbauer symmetry classes says us how many topological different ...
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0answers
395 views

Bogoliubov - de Gennes Hamiltonian and Zeeman energy

For my system I can write down the Hamiltonian in this form: $$ H = \begin{pmatrix} \epsilon_{1\downarrow}-\mu_{B}B & 0 & 0 & 0 \\ 0 & \epsilon_{2\uparrow}+\mu_{B}B & 0 & 0 \\ ...
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58 views

Difference between RPA and generalized RPA

The random phase approximation (RPA) is an approximation method in condensed matter physics and in nuclear physics. What is the difference between RPA and generalized RPA?
3
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1answer
198 views

confusion in discrete transform to solve kronig penney matrix equation in fourier space

I have a periodic potential $$V(x) =\sum_{K}e^{iKx}V_{K} =\sum_{n}e^{\iota2\pi nx/a}V_{n} $$ where $K =\frac{2\pi n}a$ is the reciprocal lattice vector and $a$ is the lattice constant and $n =\pm ...
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0answers
65 views

Chiral Landau's fermi liquid theory in 3+1D

In standard LFL theory, the effect mass of quasiparticle is different from the composite Fermion's mass. It seems that this is no longer true in Chiral case (e.g. a finite density system with ...
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0answers
106 views

physical intuition behind quasi-bound state formation in feshbach resonance

In Feshbach resonance, by scattering theory formalism it is found that the resonance in cross-section happens when bound state energy of the closed channel is near to the scattering state energy of ...
3
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1answer
161 views

Difference between Wigner crystal state and fractional quantum Hall (FQH) state

Wigner crystal and FQH effect are both due to strong electron-electron interaction under magnetic field. As we know, Landau's symmetry-breaking cannot be used to describe FQH state. But can it be used ...
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48 views

how is feshbach resonance potential term physically produced?

In Feshbach resonance model, a 2*2 potential term with space dependent diagonal and non-diagonal terms is written $\left(\begin{array}{cc} V_{11}(\mathbf{r}) & V_{12}(\mathbf{r})\\ ...
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1answer
188 views

How to determine the orientation of the massive Dirac Hamiltonian?

In the calculation of the Chern number within a 2D lattice model, let's take the Haldane model for example, the Chern number$=\pm1$ has 2 contributions coming from 2 Dirac points described by ...