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

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Griffiths phase

What are Griffiths effects in the context of condensed matter physics? From a cursory examination of the literature I've gathered the following: it seems that ordered systems have a "clean" critical ...
8
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109 views

Is there a database or a classification of High-temperature superconductors?

I was wondering if there exists a list with all (or most of) the High-$T_c$ superconductor materials. In particular I'd like to know if there are databases or review that classifies them by their ...
8
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175 views

Mean-field theory : variational approach versus self-consistency

I have a general question concerning mean-field approaches for condensed matter classical of quantum statistical mechanic systems. Does determining the mean-field by a variational approach always ...
7
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1k views

Why do Fermi liquids have T^2 resistivity?

I have often read that metals that are Fermi liquids should have a resistivity that varies with temperature like $\rho(T) = \rho(0) + a T^2 $. I guess the $T^2$ part is the resistance due to ...
7
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359 views

Is the “particle number” of “electrons” well defined in Wen's string-net theory of elementary particles?

According to professor Wen's string-net theory, electrons can be viewed as the elementary excitations of string-net objects. Just like the phonons and magnons are the elementary excitations of ...
7
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407 views

Descent equation and anomaly polynomial

I am just reading Ryu, Moore and Ludwig's paper on classifications of topological insulators and quantum anomaly. They are trying to relate the quantum anomaly as a signal of the presence of a ...
6
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163 views

Is there a way to obtain an RG flow equation for Quantum spin systems using MERA

We restrict ourselves to ground states of translationally invariant 1d quantum systems. I understand that there is the scale invariant MERA(multiscale entanglement renormalization ansatz) which ...
6
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349 views

Strong interacting v.s. Strong Coupling v.s. Strong Correlated

One of the active research areas in present is Strong interacting, Strong Coupling, Strong Correlated regime of the phases of matters. It seems to me that some physicists in the fields often mix the ...
6
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607 views

Exact diagonalization by Bogoliubov transformation

I am developing a model of multiple gaps in a square lattice. I simplified the associated Hamiltonian to make it quadratic. In this approximation it is given by, $$ H = \begin{pmatrix} \xi_\mathbf{k} ...
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177 views

Finding difficulties in taking continuum limit in nonlinear sigma model

I am learning nonlinear sigma model from Assa Auerbach's book "Interacting Electrons and Quantum Magnetism" and getting some difficulties in taking continuum limit. I am following chapter 12: The ...
5
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36 views

Lattice parameters and basis vectors of crystal lattice structures

Does someone know where I can find lattice parameters and basis vectors of crystal lattice structures (Strukturbericht Designation) for different materials? In particular I am searching the lattice ...
5
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91 views

Effective theory of topological insulator in coulomb impurity

I am trying to solve for the Haldane model with a coulomb impurity at one site in the effective theory approach and look for some topology in the solutions of the wave functions. The Hamiltonian near ...
5
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77 views

How to perform stroboscopic measurements for Floquet topological insulators?

Floquet topological insulators (arXiv:1008.1792, arXiv:1211.5623) have attracted much research interests in condensed matter physics. The goal is to realize topological insulators from trivial ...
5
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83 views

Green's function for moving solidification front

Consider a liquid solid interface $z =\zeta(x,t)$ moving at constant speed $v$, for a two dimensional problem. Due to solidification interface is changing it position. For simplicity heat ...
5
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455 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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154 views

Confusion regarding field operators

Second quantisation of the scalar field leads to an algebra of quantum field operators $$ [\phi(x),\phi(y)] = 0, \ \ [\pi(x), \pi(y)] = 0, \ \ [\phi(x),\pi(y)] = i\hbar \delta(x-y). $$ Where the field ...
5
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155 views

Third-order topological quantum phase transition in p+ip superfluid

A two-dimensional spinless non-relativistic p+ip superfluid undergoes a quantum phase transition between the BCS (weakly-coupled) and BEC (strongly-coupled) regimes. This transition is driven by ...
5
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350 views

Significance of Dirac cones in condensed matter physics

In condensed matter physics, Dirac cones can be found in graphene, topological insulators, cuprates, and iron-pnictides. This means that electrons behave as massless particles near the Dirac points. ...
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208 views

What happens to a Luttinger liquid under time reversal?

Suppose you a have an ordinary Luttinger liquid with $$ H = \int dx \sum _{\eta= \pm 1 , \sigma =\uparrow,\downarrow } \psi^\dagger_{\eta, \sigma} (x) (-i v \eta \partial _x) \psi _{\eta,\sigma} (x). ...
4
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56 views

Derivation of TKNN's main result from Kubo formula

I have a question about a small but meaningful (to me at least) step in the original TKNN paper (http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.49.405). I understand the construction of the ...
4
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54 views

In what circumstances, can exchange interaction acquire temperature dependence?

Heisenberg exchange interaction (sometimes called as magnetic stiffness?), originating from the Coulomb interaction and the Fermion statistics, is widely used in theories of magnetism. Conventionally, ...
4
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69 views

${\phi}^4$ description of Ising ferromagnet

Suppose the coupling between two spins is $C_{i,j}<0$, then the classical partition function is given by $$Z=\sum_{\{s_i\}}e^{\sum_{i,j}s_iK_{ij}s_j+h\sum_{i}s_i}$$ where $K_{ij}=-\beta C_{ij}$ and ...
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46 views

What is the difference between primary and non primary order parameter?

I found that antiferomagnet has non-primary order parameter and I don't know what is the main feature of (non-)primary order parameter?
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74 views

The wavefunction of the superconductor A consists of two parts: B and C

In reading this article, I come across this paragraph: The pink marked place is where I can't understand, why can we use direct product of the former but not the later? This is may be a basic ...
4
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200 views

Grand canonical Hamiltonian

How to explain introducing "grand canonical" Hamiltonian $$ \hat{H'}= \hat{H}-\mu \hat{N} $$ when we study a quantum system with fixed chemical potential? I understand such a substitution in a ...
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109 views

What theory describes high temperature superconductivity more sucessfully?

We know that there are so many theories on the high temperature superconductivity in cuprate. E.g. the U(1)/SU(2) gauge theory description of doped Mott insulator[Lee, Nagaosa, Wen], the phase-string ...
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173 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 ...
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93 views

What is the relation between pseudogap and time reversal symmetry breaking?

Some papers concerning high-$T_c$ superconductor discuss the pseudogap and time reversal symmetry breaking. My questions are: What is the characteristic of order-parameter in pseudogap? How to ...
4
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145 views

Eigenvalue of the adiabatic Hamiltonian of Farhi's three qubit 2-SAT problem

I was trying to reproduce example 3.3 of Quantum Computation by Adiabatic Evolution by Edward Farhi et. al. This is an adiabatic algorithm to solve an instance of three qubits 2-SAT problem. I think ...
4
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55 views

How to distinguish Bose glass and superfluid phases in a harmonic trap?

In mean-field study of Bose-Hubbard model in an optical lattice, what parameter can be calculated to distinguish Bose glass and superfluid in a harmonic trap?
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108 views

Topolgical insulators order parameter

For topological insulators Is there any way to define order parameter for topological phase transitions?
4
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1k 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} ...
4
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256 views

Some ambiguous points on Spontaneous Symmetry Breaking (SSB)?

Almost in every textbook of condensed matter physics, the standard description of SSB could be formulated as follows: Consider the lattice Heisenberg model in an external magnetic field ...
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413 views

Toward the establishment of non-equilibrium (quasi-equilibrium) magnon BEC theory

In 2006, Demokritov et al have reported that they have achieved the observation of quasi-equilibrium magnon Bose-Einstein condensation (BEC) in YIG at finite (room) temperature by using the method ...
4
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105 views

Is there a critical order of the Abelian gauge theory in (2+1)D

In (2+1)D spacetime, it is known that the $U(1)$ gauge theory is always confined (according to Polyakov), while the $\mathbb{Z}_2$ gauge theory can support a deconfined phase. Now consider a generic ...
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198 views

What is Resonance Width? Why we use it to distinguish different Regimes of the Anderson Model

The single inpurity Anderson Hamiltonian is ...
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619 views

Goldstone modes and Heisenberg model

The ideia is to show that, because of Goldstone modes, 2d systems are quite different from 3d ones. So, considering the Heisenberg model, I'll post here what I'm asked to and my current thoughts on ...
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69 views

Understanding various types of motion

In classical statistical mechanics, given a system of particles, one often goes about classifying various dynamics (or types of motion) the system may exhibit on different time scales, but studying ...
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38 views

Manking sense of an entropy equal $k_B\frac{1}{2}\ln(2)$

In problems of impurities coupled with electrons in a conduction band, like the Kondo model, is common to represent the entropy contributed by the impurity, in terms of bits, i.e. in units of ...
3
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31 views

Calculation of Berry's phase due to monopole tunneling event of $O(3)$ NLSM on square lattice

I am currently reading the seminal paper by Duncan Haldane: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.61.1029 In this paper, he asserts that for a unit-vector field ...
3
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64 views

Linear Classical Field Theories: a Mathematical Classification

Central to a mathematical understanding of the Bogolyubov transformation is the study and classification of linear lattice field theories. What follows might be familiar to many people, but I just ...
3
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62 views

Few questions regarding String-Net theory and the Standard Model

A friend today showed me this post and after reading Prof. Wen's answer, few questions came to my mind. Prof. Wen says: all fermions (elementary or composite) must carry gauge charges (see ...
3
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26 views

Tight binding hamiltonian (semi empirical) for a doubly degenerate band

For some monoclinic crystal, which has two atoms per unit cell, and its HOMO described by the doubly degenerate representation, E2u: how does one deduce the tight binding parameters from ab initio DFT ...
3
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62 views

What is physically irreducible representation?

When I use bilbao crystallographic server recently, I noticed a notation called physically irreducible representation. Paper says it is a direct sum of two complex conjugate representations (if ...
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20 views

Obtaining a Positive Hall Coefficient for Electrons Near the Top of a Valence Band

Using a Drude model of charge carriers with a charge $q$ and a mass $m$ (which I allow to take either sign at this stage) in a sample with an applied electric field $\mathbf{E}$ and magnetic field ...
3
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35 views

Weyl semi metal vs entanglement entropy

In 2+1D, entanglement entropy (EE) is crucial for identifying a topological phase. What happens in 3+1d case? e.g. what are the behaviours of EE in WSM and trivial states?
3
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69 views

What are fragmented condensates?

It is defined that if more than one eigenvalue of the one-body density matrix are macroscopically occupied the condensate is said to be fragmented. $$ n^{(1)},n^{(2)},...=\mathcal{O}(\mathcal{N}) $$ ...
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86 views

Superconducting Order Parameter and Time Reversal Symmetry

How to understand the following definition of a time reversal operation $K$ given in the review by Sigrist and Ueda: $$K a_{\mathbf{k},s}^{\dagger} = \sum_{s'} (-i\sigma_y)_{s,s'} a_{-\mathbf{k},s'}$$ ...
3
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71 views

Is $PT$ always a symmetry in (2+1)D?

Is the combination of parity $P: (x,y,t)\to (-x,y,t)$ (sometimes also called reflection $R$) and time reversal $T: (x,y,t)\to (x,y,-t)$ always a symmetry in (2+1)D theories with Lorentz or Galilean ...
3
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56 views

Can the occupation of Floquet bands be calculated from the Keldysh Green's function?

A periodically driven band structure can be semiclassically described by Floquet theory, resulting in photon-dressed Floquet bands (non-equilibrium steady states). Usually, for non-equilibrium ...