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

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What is the physical origin of van Hove singularity?

I am trying to build physical intuition about van Hove singularities. The density of states for a system with energy dispersion $E_\vec{k}$ is defined as $$ D(E) = \int_{S(E)} \frac{dS}{4\pi^3} ...
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22 views

Problem in deriving the second term in perturbation expansion the quantum ising model

So I'm trying to derive the perturbation expansion for one particle states in the quantum ising model (Sachdev 2011 QPTs which this is derived from ) $$ H_I= - J g \sum_i \sigma_i^x - J ...
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55 views

If a liquid is compressed enough, would it become solid?

If a liquid were to be compressed so tensely that the particles had no room to move, would it then become a solid? Also, would the same happen with a gas?
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13 views

Deformation in the nematic phase of a liquid crystal survived in solid state

Does anyone know if I cool a liquid crystal with a deformed nematic phase quickly it will preserve the deformation in the crystal lattice? I didn't never see that in classical books on liquid ...
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30 views

Electric polarization in terms of berry phase?

I was reading a text in which Electric polarization in terms of Berry phase was defined as $P=\frac{e}{2\pi}\sum_{n}\int A_n (k) dk$ under gauge transformation $P\rightarrow P+ne$ (which means ...
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32 views

Four dimensional Bravais lattice

I am wondering if there are any reference on four dimensional Bravais lattice and their primitive vectors, even an example will help.
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27 views

Why the heat capacity doesn't diverge in the Kosterlitz-Thouless (KT) phase transition?

The KT transition has a special properties that, during the phase transition the heat capacity stay finite (so the behaviour of the heat capacity cannot reflect any critical behaviours). However, the ...
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72 views

which are the non-abelian anyons for universal quantum computation

I am trying to get a list of non-abelian anyons that can be used for universal quantum computation by implementing gates via braiding. I found that Majorana fermions and para-fermions (not sure about ...
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59 views

Chiral Fermion Problem and the String Net Model

In Xiao-Gang Wen's book "Quantum Field Theory of Many-Body Systems", he mentions that (the string-net condensation picture)...has a problem: we do not yet know how to produce the $SU(2)$ part of ...
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49 views

Recommendations for Advanced Books on the Interface between CMT and Quantum Information

I am looking for a book/review article/website which covers applications of condensed matter theory to quantum information. In particular, I am interested in such topics as a mathematical description ...
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71 views

Is Chern-number for free fermion system always limited by total band number, i.e. number of orbits with a unit cell?

If so, how to see that? Also I think it has been proven that the total Chern-number for free fermion system is 0? If you know how to prove it, please make some comment or hopefully a sketch of ...
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34 views

Particle hole symmetry of single site?

Let's consider I have a system with equal number of spin up and spin down particles Now I consider a single site of system,I have a state $c_{i\uparrow} ^{\dagger}\mid 0\rangle$ under particle hole ...
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65 views

Can a symmetry-preserving unitary transformation that goes from a trivial SPT to a non-trivial SPT be local?

This question concerns the very interesting paper: ''Symmetry protected topological (SPT) orders and the group cohomology of their symmetry group'' by Chen et al., http://arxiv.org/abs/1106.4772 In ...
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34 views

Definition of Fourier Transform on a Lattice

I am reading a book(EDIT: the book is Czyholls theoretical condensed matter physics, though i am not sure if there is an english version) where for periodic functions $f(x_l+L)=f(x_l)$ the Fourier ...
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2answers
36 views

Is the photon truly not absorbed in Raman scattering?

In reading about Raman Scattering, I was thinking while reading it "okay, incident photo absorbed by molecule, molecule goes to higher energy vibrational state, molecule re-emits photon with either ...
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2answers
38 views

Is molecular vibration just phonon modes for a single molecule?

I'm reading about Raman Scattering, of which a big part is measuring the energy lost to/gained from Molecular Vibrations. I wasn't totally clear on exactly what is "vibrating" in vibrational modes (is ...
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1answer
50 views

How to compute the density of state from the Green function?

I'd like to plot the density of state (DOS) for a specific system, say an s-wave BCS superconductor, the Green function of which is ...
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22 views

Effects of cutting carbon nanotube buckypaper

Carbon nanotube buckypaper is a film/paper made from a mesh of carbon nanotube fibers, where each fiber is a bundle of a couple hundred nanotubes. This paper is flexible and tough like normal paper, ...
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71 views

Symmetry of Bloch Hamiltonian

If a crystal system preserve a symmetry C, why its Bloch Hamiltonian satisfy $H(C\vec k)=CH(\vec k)C^{-1} $
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31 views

Density of particles in hexagonal lattice

I need to calculate, in a 2D hexagonal lattice of point particles in which the nearest neighbours are a distance apart $a$, what's the density of particles. What I really need is, if $\rho$ is the ...
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34 views

Symmetry arguments for valley physics in graphene with broken inversion

I am trying to understand this paper: http://link.aps.org/doi/10.1103/PhysRevLett.99.236809 (Here is an arXiv version: http://arxiv.org/abs/0709.1274) In the introduction, they mention certain ...
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74 views

What happens to the planck distribution if the temperature is set to zero?

BE Problem I am currently working on modelling the density of states and optical conductivity of graphene utilizing the GW algorithm. In calculating the exchange self energy of the system, the ...
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1answer
57 views

Topological entanglement entropy in transverse quantum Ising model?

I have seen from literature that the $Z_2$ lattice gauge theory in 2d could be mapped into a quantum Ising model with gauge constraints on the Hilbert space by dual transformation. The deconfined ...
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101 views

Green's function for 1 D hubbard model?

Consider the 1D two-site Hubbard model at half filling $H=-t\sum _{\sigma} (c_{1\sigma} ^{\dagger}c_{2\sigma}+h.c.)+U\sum_i(n_{i\uparrow}-\frac{1}{2})(n_{i\downarrow}-\frac{1}{2})$ where the sum is ...
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1answer
83 views

Edge states for SSH model?

We can write the Hamiltonian for SSH model as $H=\sum_i(t+\delta t)c_i^{\dagger} c_{i+1}+(t-\delta t)c_{i+1}^\dagger c_i+h.c$ We know that there are two topological phases $N_1=0$ for $\delta ...
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61 views

What is the reason for chiral anomalies in condensed matter systems?

If you consider a massless relativistic fermion theory and you perform a chiral transformation, then you realize that while the classical action remains invariant under this transformation the ...
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60 views

Density Matrix Renormalization Group (DMRG) Simulation of a String-Net Model

In the following paper, Dr. Xiao Gang-Wen et. al. introduce the idea that string-net condensed states can be represented in terms of tensor product states: http://arxiv.org/pdf/0809.2821.pdf The ...
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32 views

Mixed spin Ising Model

As we know ferrimagnets can be modeled by the Ising model. I came across this equation in "Compensation Temperature of the Mixed-Spin Ising Model on the Hexagonal Lattice" by W. Figueiredo, M. Godoy, ...
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19 views

Pauli Master Equation usable for Bose-Einstein condensation?

As I am not an expert in the field, please correct me accordingly. Now to my problem: I wondered whether it is justified to use the Pauli Master Equation (i.e. linear coupling to markovian ...
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What is the volume magnetization of Fe3O4 (magnetite) monodomains at room temperature?

Magnetite is great stuff for making ferrofluids and has a huge amount of literature. Yet I can't seem to find an answer to the simple question in the title. The magnetization of various bulk ...
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1answer
35 views

Paramagnetic/ferromagnetic transition under a magnetic field

The paramagnetic/ferromagnetic phase transition is an archetypal example of a continuous (or second-order) phase transition. When the temperature $T$ approaches the Curie temperature $T_c$, the ...
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30 views

Intuition behind modeling quantum impurities as two-level systems

I've been trying to get a basic understanding of quantum impurity problems, starting with the Anderson model. The Wikipedia article (along with some review articles) seems to explain the simplest ...
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68 views

Evaluation of Green function for two site system?

Let's consider I have two site system whose hamiltonian has $2\times2$ matrix form. In general we can write the Green function for above Hamiltonian as $G^{-1}=i \omega-H $ or $G=[i\omega-H]^{-1}$ and ...
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80 views

How to show time reversal symmetry does not break in the tight binding Hamiltonian for the honeycomb lattice?

The Hamiltonian of the honeycomb lattice is $$ H=\sum_{k\sigma}t(k) a_{k\sigma}^\dagger b_{k\sigma}+h.c $$ Where $t(-k)=t^*(k)$. If we do a time reversal transformation(according the answer to this ...
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56 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 ...
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27 views

What are the limitations of simulating grand unification theories of elementary particles in condensed matter settings?

What are the limitations of simulating grand unification theories of elementary particles in condensed matter settings? I know that condensed matter systems can be constructed to be described by any ...
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31 views

Time Reversal Bulk Hamiltonian

This questions is from pages 68 and 69 of: http://fizipedia.bme.hu/images/1/14/Topological_insulators.pdf For a lattice, time reversal invariance of the bulk corresponds to the equation (Eqn 6.11): ...
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19 views

Constructing uniform mesh in reciprocal space?

This is a bit of a mental exercise for me to get comfortable with the math of reciprocal spaces since I am going to start doing some research that requires knowledge of reciprocal spaces. Let's say I ...
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61 views

Deriving effective model without integrating out degrees of freedom in path integral formalism?

In path integral formalism of quantum field theory (particle physics or condensed matter), one can in principle integrate out part of the degrees of freedom so as to attain an effective model ...
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37 views

What is the importance of reciprocal lattice?

Reciprocal lattice is the diffraction plot of a crystal. Now with the STM instrument we can get the get the topology of the crystal, so what is the importance of reciprocal lattice or the Brillouin ...
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52 views

Tight binding model in a magnetic field

The standard way to treat a tight binding method in a magnetic is to replace the hopping matrix element: $t_{i,j}\rightarrow e^{i\int_i^j\mathbf{A(x)}.d\mathbf{x}}$ the so called "Peierls ...
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1answer
35 views

Question regarding NaCl equilibrium separation

So I am tutoring someone later and one of the problems is from Eisberg/Resnick Ch 12. The potential energy $V$ of NaCl can be described emperically by $$V = \frac{-e^2}{4\pi\epsilon_0 ...
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47 views

Why talking BCS Hamiltonian doesn't conserve particle number?

The BCS Hamiltonian reads: $$H_{BCS}=\sum_{k\sigma}\epsilon_k c_{k\sigma}^\dagger c_{k\sigma}-\Delta^*\sum_k c_{k\uparrow}^\dagger c_{-k\downarrow}^\dagger+h.c.$$ The particle number operator reads: ...
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50 views

Why the non-analyticity of free energy function implies phase transition? And what's its connection with other 'higher level' free energies?

I have seen 'free energy' arising from several contexts in very different forms, and each contains different amount of information. For example free energy is defined as the logarithm of the ...
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48 views

How does one find the phonon frequencies for a 1D anharmonic interaction potential?

Suppose there is a one-dimensional crystal with an anharmonic interaction potential between particles (e.g. $U = ax^2+bx^3$ where $x = d-a$ with $d$ as the distance between two particles and $a$ as ...
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67 views

Is the superconducting current made up of Cooper pairs?

Inside the superconductor it should be $\mu_0\mathbf{j} = \mathbf{\nabla} \times \mathbf{B} = 0$, since B is 0 due to the Messner effect. This means that the current is carried by the surface. But ...
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116 views

Chiral anomaly in Weyl semimetal

In the presence of electromagnetic fields $E$ and $B$, four current is not conserved in a Weyl semimetal i.e. $\partial_{\mu} j^{\mu}\propto E\cdot B \neq 0$. There are some proofs in the literature ...
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42 views

Angle-resolved photoemission spectral (ARPES) function from band Hamiltonian

I am trying to derive spectral function for a band Hamiltonian. I am using http://arxiv.org/abs/cond-mat/0306084 as a prototype reference. I do not understand how the coherence factors $u_k$ and $v_k$ ...
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26 views

XRD of Graphene Foam

At what 2$\theta$ values Graphene Foam shows the peaks in XRD ? I got two peaks at 2$\theta$ values 14.7 degree and 17.2 degree..
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49 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 + ...