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

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Why use coherent state path integral? What is its motivation or goal?

In almost all textbooks of quantum field theory for high energy, they insert the position and momentum eigenstate to formulate the path integral. While in condensed matter field theory, they insert ...
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18 views

Antiunitary operators in the tenfold way

In the classification of free fermion systems in condensed matter, physicists usually divide the systems into ten symmetry classes, first discovered by Altland and Zirnbauer. In their classification, ...
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Are symmetries of a degenerate ground-state manifold always broken?

If a Hamiltonian has a global symmetry and a degenerate ground state, then in the thermodynamic limit, the ground states $| \psi \rangle$ that are eigenstates of the symmetry operator typically become ...
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31 views

Phonon softening explanation

Is there a simple, intuitive answer of why phonons soften with strain? I am aware of the Grüneisen parameter but it just tells us there is a negative sign.
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12 views

Showing that the Yang operator creates an elementary excitation in the 1D Hubbard model using EOM approach

Hamiltonian of the 1D Hubbard model: $ H = -t \sum_{\langle i,j \rangle,\sigma}( c^{\dagger}_{i,\sigma} c_{j,\sigma}+ c^\dagger_{j,\sigma}c_{i,\sigma}) + U \sum_{i=1}^N n_{i\uparrow} n_{i\downarrow} ...
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95 views

Weaker Formulations of Bulk-boundary Correspondence for Interacting Systems

From this post, it seems that bulk-boundary correspondence does not hold in general for interacting systems. What is meant by bulk-boundary correspondence there appears to be the existence of robust ...
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30 views

What is the difference between Bosonic and Fermionic symmetry protected topological phases (SPT)

I am reading the paper ``Braiding statistics approach to Symmetry Protected Topological Phases'' by Levin and Gu. In this paper two spin models considered describe spin-1/2 particles in (1+2) ...
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9 views

difference between weak and strong topologiccal insulators

Does someone know what the difference is between weak and strong topological insulators? (And do both exist in any dimension?).
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15 views

Fermi surface reconstruction and fermi pockets

Certain quantum phase transitions are characterized by the emergence of some ordering wavevector $K$ : antiferromagnetism, charge or spin density waves, among others. In the case of Néel ...
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Why don't FCC metals have a brittle-to-ductile temperature transition?

I initially thought that it had something to do with the number of slip systems in FCC vs. BCC, but they're both the same.
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279 views

Does the low-energy gauge structure depend on the choice of $SU(2)$ gauge freedom?

The starting point and notations used here are presented in Two puzzles on the Projective Symmetry Group(PSG)?. As we know, Invariant Gauge Group(IGG) is a normal subgroup of Projective Symmetry ...
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27 views

Paradox in topological phase of SSH model

Consider the SSH model, i.e. the dimerized tight-binding model with Hamiltonian $$H = \sum_i (t+\delta t) c^\dagger_{Ai} c_{Bi} + (t-\delta t) c_{A(i+1)}^\dagger c_{Bi} + \text{h.c.}.$$ This describes ...
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19 views

What is Landau-deGenes Expansion?

I am an undergraduate student in an introduction to condensed matter physics course and I am struggling to understand the process of Landau expansion of order parameter S as it relates to liquid ...
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257 views

Superconductivity in graphene with spin orbital coupling, is it proper to let the order parameter on two sub-lattice equal?

I am reading this article: Edge superconducting correlation in the attractive-U Kane-Mele-Hubbard model. Considering just the first part of the article, where a negative-U Hubbard model with the ...
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322 views

Atomic nearest neighbor notation

I recently got a correction to a paper that I am writing. The correction references a section in which I talk about nearest neighbors. The comment says: Do you mean NN, NNN, etc., or NN, 2NN, 3NN? ...
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43 views

Majorara zero mode in Ising chain, not exactly zero subtlety

We know the transverse field Ising model with N sites(open boundary), can be mapped into N free fermions(there are 2N modes if including the negative energy counterparts) With property: ...
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19 views

The existence Water nanoparticles [closed]

Has anyone investigated the properties of water nanoparticles? If yes what are those? If not, why not?
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13 views

Velocity matrix and non-local pseudo potentials

It is known that velocity of bloch wave functions are related to band energy derivatives: $$v(k)=\frac{1}{\hbar}\frac{\partial \epsilon}{\partial k}$$ However, in the following paper, it is given ...
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Kitaev chaing, time reversel symmetry, particle hole symmetry

I was wondering if the Kitaev chain has time reversal symmetry. I think it probably doesn't because by staking Kitaev chains it is possible to create a so called Chern insulator with propagating ...
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18 views

Energy (voltage) correction on energy level between metallic electrodes with dielectric and accounting for work function difference

My goal is to understand how to correct for the field drop and the work function difference when performing electrical measurements on a certain energy level of a sandwiched system. The situation is ...
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1answer
26 views

Why is hot wood ash more fluid than cold ash?

When I remove ash from my fireplace I do so by scraping it away through holes about 5 millimeters wide in the fireplace floor. Whenever the ash is hot, it definitely feels much more fluid than when it ...
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2answers
32 views

Lowest energy product state of a local hamiltonian

Lets consider one-dimensional spin chain with periodic boundary condition and $N$ sites. We are given a translationally-invariant local hamiltonian $H$ which is defined as $H=\sum_{i=1}^N h_{i,i+1}$, ...
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1answer
19 views

Exponential decay of correlation in PEPS

PEPS (Projected Entangled Pair State) is a tensor network that plays the same role in two dimensional lattice as MPS (Matrix Product State) plays in one dimensional spin chain. A good introduction can ...
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220 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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185 views

How does crystal lattice explain electrical conductance?

From http://education.jlab.org In a metal, the atoms are arranged in a crystal-like configuration. ... Now, in a metal, the valence band is relatively close to the conduction band - ...
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23 views

Inversion symmetry points of graphene

I have question about graphene. When you have the graphene lattice two types of atoms can be distinguished, let's call them type A and B.You can draw a unit cell that has the shape of a ...
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59 views

Cooper pairing from repulsive potential

Suppose the Hamiltonian of a many-electron system consists of a potential which is repulsive : $\langle k_1, k_2 |\hat V |k_1',k_2' \rangle > 0$ where $k_1, k_2, \cdots$ are possible momenta that ...
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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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1answer
35 views

Adiabatic transition from superfluid to Mott insulator?

I have a question about the dynamical passage from superfluid to Mott insulator state in the Bose-Hubbard model. Is it possible to go from superfluid region to the Mott insulator by changing the ...
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28 views

Reason behind heating the substrate in Pulsed Laser Deposition

Why do we need to supply a constant heat to the substrate while depositing thin films in Pulsed Laser Deposition technique?
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17 views

Separation of center of mass and relative frame for 2 particles in Haldane model in coulomb impurity

In the following paper http://journals.aps.org/prb/pdf/10.1103/PhysRevB.81.045428 the author says that the center of mass and relative motion cannot be decoupled. But the Hamiltonian can be separated ...
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647 views

Why do electron and hole mobilities decrease with temperature?

From page 35 of "Microelectronics" by Millman Grabel Mobility $\mu$ decreases with temperature because more carriers are present and these carriers are more energetic at higher temperatures. ...
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61 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 ...
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27 views

Drude Conductivity of Graphene

Use the Drude model to estimate the low temperature conductivity of a sheet of graphene, up to a dimensionless constant. (Assume the electron dispersion relation is $E(\mathbf{k})=\hbar ...
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Is a phason a Goldstone mode?

Suppose we have a lattice system whose ground state is an incommensurate charge-density wave. Strictly speaking, this ground state does not have Goldstone modes because the only symmetry that is ...
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16 views

Quantum Hall effect in a Corbino disk

I'm a little bit confused about the Quantum Hall effect. I follow a course in condensed matter physics and the Quantum Hall effect is seen as the mother of all effects in condensed matter physics ...
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1answer
176 views

Tight binding Hamiltonian for 2D finite dimensional lattice and nanowire

The Hamiltonian of a 1D lattice having finite $N$ atoms, (if we consider one basis per atom) is given by the following $N\times N$ matrix- Here $E$ is the onsite energy and $t$ is the hopping ...
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627 views

Peierls substitution vs minimal coupling

In the presence of vector potential (let's assume it's uniform), a tight-binding Hamiltonian will be changed according to the Peierls substitution: $$t_{ij}c_i^{\dagger}c_j \to ...
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Numerical Tools to find Braiding Statistics of Quasiparticles

While certain classes of systems that exhibit topological order can be solved exactly (such as the Toric Code, Abelian FQH Edges, etc.) there also exist systems (think of perturbed versions of the ...
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415 views

Distinguishable, Indistinguishable Paramagnetic Ideal Gas

In the canonical ensemble, the partition function for an ideal gas is given by: $$\frac{Z}{N!}$$ The factor $N!$ accounts for the indistinguishability of the particles of the ideal gas. What ...
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1answer
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Clockwise and Anti-Clockwise next-nearest hopping on honeycomb lattice?

I have the difficulty of understanding, How we can distinguish that which next-nearest hopping on honeycomb lattice is clockwise or anticlockwise?
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1answer
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Semiconductor nanostructure and heterostructure

What is the difference between compositional superlattice and doping superlattice?
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11 views

Effect symmetry on points in momentum space

I have to study some material for a condensed matter physics course and cam across a passage that I don't understand. "In momentum space time reversal symmetry and particle hole symmetry only have ...
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12 views

effect of inversion symmetry on the bandstructure

I have a very general question, but I hope that someone can answer it. Can someone describe what the effect of inversion symmetry is on the bandstructure. (Or is there not a general effect?). ...
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320 views

Quantum Hall Effect and Edge States

In quantum hall effect we measure the hall conductance (in transverse direction) which is quantized. My question how do they take care of the edge states that are in the longitudinal side?
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53 views

What does it mean for a topological phase to be “symmetry protected”?

I have seen some very nice and enlightening awnsers to questions related to topological order and insulators, such as here, or here. However, I'm still puzzled by the concept of "symmetry protection" ...
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51 views

What's the origin of electrical resistance?

i know relation ohm : $$R=\rho\frac{L}{A} $$ i want to know about resistance from view point small particle like atom,dipole: when we have a resistor,with a special voltage it has loss power: whats ...
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179 views

How to prove Bloch function is periodic in reciprocal lattice?

How to prove Bloch function is periodic in reciprocal lattice? I saw in some textbooks this formula: $$ \Psi_{\mathbf{k}} (\mathbf{r}) = \sum_{\mathbf{G}} ...
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56 views

Symmetries in physics (specifically condensed matter physics)

Symmetries play a big role in physics. Some symmetries are translation symmetry, rotation symmetry, time translation symmetry, timereversal symmetry etc. It seems that in condensed matter physics ...
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Super conductivity and energy gap in fermionic/bosonic subspaces

I am trying to understand the phenomena of super-conductivity from a broader level. What I understand for now is that for super-conductivity to be possible in a system, a necessary requirement is that ...