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

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Conformational Analysis of Ethane and Butane

How does a condensed matter theorist explain conformations of Ethane and Butane using tools from Quantum field theory? If they don't how do they calculate energy differences and predict differences ...
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Why electron phonon interaction happends near fermi surface?

Usually the energy correction to electron by electron phonon interaction in metals at zero tempreture has the form(Gerald D.Mahan Many-Particle Physics, Third Edition, Sec. 7.4) $$ \sum(k,u)=\int\frac{...
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How to understand the idea of functional renormalization group?

I have been looking at how to use the functional RG method in many-body systems, but I don't quiet get the idea of it, it look different from Wilson's RG approach (eg. why shall we integrate out the ...
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39 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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44 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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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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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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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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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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82 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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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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Where can I learn about band theory?

I'm studying quantum mechanics and I want to understand perfectly where the bands of the electronic sturcture come from. I've read that it is related with the periodic potential, Bloch waves and ...
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51 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: $$\gamma^\...
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33 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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30 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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35 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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19 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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56 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 parallelogram....
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77 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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107 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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84 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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28 views

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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51 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 v_F|\mathbf{k}|...
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27 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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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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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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Semiconductor nanostructure and heterostructure

What is the difference between compositional superlattice and doping superlattice?
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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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25 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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108 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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60 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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49 views

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 ...
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Construction of a lattice structure and the Wyckoff positions

I would like to build a unit cell of a Cmcm (no. 63) lattice structure. It is a orthorhombic crystal and my lattice vectors are $\vec a_1 = (1,0,0)\,,\; \vec a_2 = (0,3,0)\,, \;\vec a_3 = (0,0,2)\,.$ ...
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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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Where should I start learning Landau's theory of superfluidity?

Where should I start learning Landau's theory of superfluidity? For a second year undergraduate.
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75 views

Bogoliubov transformation with two pairing terms

Let us assume that we have a Hamiltonian of the form: $$ H = \sum_{k,\sigma,s}\epsilon_{\sigma s}\left(k\right)c_{k\sigma s}^{\dagger}c_{k\sigma s} + \sum_{k,s}\Delta_{0}\left(k\right)c_{k\uparrow s}^...
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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 ...
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45 views

How does the surface of a material always break inversion symmetry?

I am trying to visualize this for an HCP structure. Take the profile view as such: just working in 2d. So my understanding is if we can take a point (x,y) -> (-x,-y) and get the same crystal than ...
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58 views

Free electron Gas shortcomings

I am studying surface states and the Rashba effect. A common model I keep coming across is to implement the free electron model. In this model we get the spin orbit interaction Hamiltonian by ...
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26 views

Can orbital angular momentum of an electron be changed?

In a lab at my university they are working on a project that deals with changing the "net magnetization" of a material by "flipping" the spins on some electrons. Is orbital angular momentum not ...
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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 $k_B\ln(...
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Surface potential and symmetry breaking

I am studying surface states currently and am a little confused about something. If I consider p-orbits on a surface state that is the top layer of an HCP structure -- I understand the hopping terms ...
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40 views

What is the source of the Curie point?

I'm seriously revisiting my knowledge on magnetism, and the Curie point has been both enlightening and mystifying. I understand what it does ((ferro)magnetism disappears above it), and have a faint ...
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41 views

Energy gap in phonons and violation of perturbation theory

In a 1 dimensional chain of similar ions which are connected to each other with similar springs there is just one corresponding frequency for each wave vector. But solving the problem of one ...
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47 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 $\hat{\Omega}(x,y,t)...
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64 views

Hubbard model within mean-field: three different approaches

While reading doi:10.1016/j.carbon.2012.03.009 , the authors mention three types of Hubbard models within mean-field approximation. The first one describes the electron-electron interaction, and to my ...
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55 views

why pseudo wave functions can be used to calculate berry connection

Berry connection plays a very important role in topological insulators. Berry connection $A(k)$ is defined to be $i\langle u(k)|\nabla_k|u(k)\rangle$, where $|u(k)\rangle$ is the periodic part of ...
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What physical properties can't be predicted based on index of refraction? [closed]

If I tell you the real and imaginary parts of the index of refraction for all frequencies, name a property that can't be predicted based on that information. If you're assuming this is a gas, specify ...