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

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What is the viscosity difference between a solid and a liquid

The pitch drop experiment, for example, shows bitumen as a liquid, even though it appears to be a solid, and then there is the "glass: solid or liquid" debate. Is there a numerical value in viscosity ...
-4
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2answers
319 views

Would I get a shock from a Weyl fermion?

I know this is only just a new discovery. I assume this new quasi particle is a form of what "electricians" call current. I wonder though if it is more like AC or DC when it comes to touching the ...
3
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1answer
55 views

How is superconducting coherence length measured in experiment?

In a superconductor, the coherence length measure the mean distance between two electrons in the Cooper pair. How is the coherence length experimentally measured?
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31 views

Excitation spectrum of heisenberg model

I understand that ferromagnetic Heisenberg model (lattice of spin variables that can point in any direction) spectrum can be deduced by a $\lambda\phi^4$ theory with $\phi$ being complex. This model ...
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49 views

Why does not the bare interaction potential appear in the Bogoliubov theory?

They use some effective potential defined by the s-wave scattering length, but not the bare atom-atom interaction $V(r)$. Why? It is standard practice in second quantization to use the bare ...
2
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1answer
58 views

e-e scattering rate in normal fermi liquid and in graphene

In Ashcroft/Mermin's solid state physics, in equation (17.64) they argued that: We expect from lowest-order perturbation theory (Born approximation) that $\tau$ will depend on the ...
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78 views

Chern number of a two-level system

The bulk of my question relates to a two-level system, but I have some questions about the Chern number in general as well. The Chern number of a gapped periodic system (free fermions or mean field) ...
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2answers
224 views

Why are band maxima / minima often (always?) at high-symmetry points?

(inspired by this question.) In every semiconductor that I can think of, the valence band maximum and conduction band minimum are at a high-symmetry point in the Brillouin Zone (BZ). Often the BZ ...
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63 views

About the definition of the spin current

People have been talking about the spin current for a while. But there is a fundamental problem. Unlike charge, or mass, spin is not conserved. Let us take the 1d spin-1/2 Heisenberg chain as an ...
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1answer
71 views

Connection between bond-dimension of a matrix product state and entanglement

The bond dimension is the dimension of the truncated matrix product state (MPS). Let us assume that I am simulating some many-body system with high entanglement via the density matrix renormalization ...
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1answer
49 views

When metal solidified, why is its surface not flat like polished?

I expect that what one can see on the outside of a just solidified piece of metal is just the "raw" surface of the inner stucture. Solidifying metals or alloys arranges in partial christal latices ...
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50 views

Is interaction a relevant perturbation for 1d Anderson localization of fermions?

Disorder is a relevant perturbation in 1d, which drives the system to Anderson localization. My question is if I am already at the Anderson localization fixed point, how to analyze the scaling ...
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1answer
45 views

Superconductor in a parallel vs perpendicular magnetic field

My question concern's the huge difference in critical fields regarding a thin superconductor(SC) which is surrounded by a magnetic field. lets imagine the SC is a thin film in the x-y Plane: Applying ...
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43 views

Gauge invariance of classical XY spin model

I am trying to understand gauge invariance as it is applied to a XY model Any ideas if it is in fact gauge invariant? Examples of how it is or isn't would be very helpful. If it is not gauge ...
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0answers
54 views

Hopping on a lattice?

Usually hopping on a lattice written as $$H=-tc_i ^{\dagger} c_{i+1} + h.c$$ where $t$ represent hopping amplitude When we consider hopping on a lattice than, Do we need at least the empty orbitals ...
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0answers
80 views

How are lattice parameters determined from reciprocal space maps?

It seems that the papers speak of reciprocal space maps with very high praise because of its ability to study strain in epitaxial films and determine the amount of relaxation. Also one can determine ...
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34 views

Chemical potential of Cooper pairs

Consider a BCS Hamiltonian with an additional term that reads: $i\mu c_k^+c_{-k}^+ + H.c$. What is the meaning of $\mu$? How one can write this term in real space, and does this term show up in the ...
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1answer
52 views

physics of the beaker experiment for superfluid helium

here is an illustration and explanation of the beaker experiment over superfluid helium: So, according to this experiment, can anyone say what is the cause? I mean the superfluids are disconnected ...
7
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2answers
173 views

Has a phonon, a formal quasi-particle, ever been observed as a point particle?

Phonons are a nice tool to simplify the quantum-mechanical description of lattice vibrations by identifying the ladder operator of normal modes as creation operators of a certain quasi-particle. In ...
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1answer
126 views

What is the theory behind spin-transfer torque?

I would like to get a layman's understanding of STT (Spin-transfer torque). By that I mean I don't have time to understand the mathematical and exact physical theory, but I would still very much like ...
2
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1answer
75 views

How is spring steel so hard?

The mechanical properties of a steel object are influenced by the metal composition, the manufacturing process, and the final heat treatment of the object. Spring steel is a steel that was heat ...
2
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1answer
71 views

Parent hamiltonian of AKLT state

Given a translationally invariant Matrix Product State (assuming periodic boundary condition) on $N$ sites of dimension $d$ each, which takes the form $\sum_{i_1,i_2\ldots ...
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41 views

Normal coordinates for harmonic approximation (classical lattice vibration)

I am reading Jenő Sólyom's "Fundamentals of the Physcs of Solids" vol. 1. and i am very much stuck at this point (chapter 11.3.2 in the book): In the harmonic approximation the potential energy of a ...
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41 views

Ground state symmetry breaking in Bose-Hubbard model with spin-orbit coupling

The Hamiltonian for 2D Bose-Hubbard model with spin-orbit coupling on a square lattice is written as $ H = -t\sum_{\langle ij \rangle}\Psi_i^{\dagger}\Psi_j^{\vphantom{\dagger}} + ...
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52 views

Wigner-Dyson vs Poisson level statistics in MBL effective Hamiltonian

Many-body localization (MBL) has been a hot topic recently. It was proposed that the MBL system can be describe by the following fixed-point Hamiltonian ...
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1answer
37 views

How does Kohn's theorem demonstrate that a rotating microwave field can only connect the ground state with the cyclotron mode?

This is a follow-up question to Proof of Kohn's theorem. I am confused about a point in the answer given by @NowIGetToLearnWhatAHeadIs. It is noted that the perturbing Hamiltonian in Equation 12 ...
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1answer
42 views

How do I evaluate the angular momentum of the wave function?

I'm working with Bose-Einstein condensates and running a 2D single component Gross-Pitaevskii equation solver for the simulations in MATLAB. The way it works is that it numerically solves the GP ...
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19 views

Reciprocal Plane diagram of body-centered cell?

I was reading that the reciprocal lattice of a body-centered cell (BCC) is simply the face-centered cell(FCC), right? Would each of the reciprocal lattice vectors be the FCC lattice vectors, but with ...
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26 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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2answers
120 views

Definition of Topological Order in terms of categories

I have a question regarding the definition of topological order as defined in Wen's review article http://www.hindawi.com/journals/isrn/2013/198710/. Is the distinction between boundary-gapped ...
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2answers
112 views

Topological superconductors: what is the role of spin-orbit coupling? Are there topological non-trivial states without spin-orbit?

Let's say I have a one-dimensional system with particle-hole symmetry and with broken time-reversal symmetry. As a consequence, the chiral symmetry is also broken in this case (the chiral symmetry ...
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16 views

How to determine film thickness in a multilayer sample

What is the mathematical derivation or formula to determine thickness of each film in a multilayer sample with the help of X-Ray Reflectivity technique?
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0answers
58 views

Convert discrete sum to principal integral

I'm studying IQHE beginning with Laughlin's famous gauge argument. I referred to his Nobel Lecture, in which he mentioned a paper that enlightened him. It is Phys.Rev.B.23.5632(1981) which talked ...
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1answer
62 views

Entanglement between the electrons in the Laughlin wave function

Consider the $1/3$-Laughlin wave function $$ \Psi \propto \exp \left(-\sum_i |z_i|^2 \right) \prod_{1\leq i<j\leq N} (z_i-z_j)^3 . $$ It cannot be written in the form of a Slater determinant, ...
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2answers
58 views

Spectral function with negative value

How does one understand a negative value in the spectral function $$\chi=-\mathrm{Im(G)}$$ where $G$ is the Green function and $\chi$ is a spectral function?
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1answer
197 views

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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34 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 ...
2
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1answer
78 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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1answer
20 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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0answers
44 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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51 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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1answer
59 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 ...
3
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1answer
97 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 ...
0
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1answer
115 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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66 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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1answer
105 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 ...
0
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1answer
68 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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3answers
122 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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55 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
57 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 ...