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

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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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20 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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35 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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21 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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2answers
29 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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1answer
18 views

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
19 views

Semiconductor nanostructure and heterostructure

What is the difference between compositional superlattice and doping superlattice?
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12 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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18 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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1answer
80 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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2answers
55 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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1answer
45 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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16 views

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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61 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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1answer
31 views

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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56 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 ...
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44 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 ...
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1answer
35 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 ...
3
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1answer
52 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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25 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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41 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 ...
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9 views

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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1answer
33 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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1answer
36 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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37 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 ...
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1answer
59 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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1answer
46 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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3answers
54 views

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 ...
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2answers
34 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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69 views

What would be the hardest material in the universe

I wonder to ask what is the potentially hardest, most solid, man-known material in the universe. I search for the most unbreakable material in the univirse. Resistant to heating included. I've heard ...
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1answer
45 views

Why is the symmetric phase in a Bose gas not superfluid?

In the theory of superfluidity in weakly interacting Bose gases, one finds that in the symmetric phase the exctitations have the dispersion relation $\omega = \frac{k^2}{2m}-\mu$ with gap ...
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1answer
43 views

Is there a spontaneous $U(1)$ symmetry breaking in atomic BECs?

In the theory of Bose-Einstein condensation, one way to define the order parameter is by using the concept of spontaneous symmetry breaking. One says that, below the critical temperature, the ...
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1answer
32 views

Ohm's law deviation

In terms of superconductivities and diodes (I do not know anything else except these), Ohm's law deviate from a linear relation. I search many titles or tags for this but I did not understand properly ...
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68 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 ...
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26 views

Role of Cavity Resonators in continuous wavelength-electron paramagnetic resonance(CW-EPR)

Why is it necessary to place the sample in a cavity resonator for obtaining EPR spectrum in CW-EPR? What role does a cavity resonator play in a CW-EPR spectrometer?
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29 views

Dopants vs impurities

The question is related to terminology. What is the difference between dopants and impurities in condensed matter (semiconductor) physics?
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1answer
39 views

Difference Between Ruderman-Kittel-Kasuya-Yosida (RKKY) Interaction and Kondo Effect

The question is in the title. I don't understand the difference between these two effects. Based on my understanding, the Kondo Effect is where the conduction electrons effectively screen a local ...
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65 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 ...
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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 ...
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18 views

Systems with these temperature dependence of thermal-conductivity

I want to find out examples for systems (of any kind) in which the temperature dependence of thermal-conductivity($\kappa_{T}$) is of type- \begin{equation} T^{-\alpha}~~~~~ where ~~~~~\alpha>0 ...
2
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1answer
49 views

Localized Phonon Vibrational Modes and Thermal Conductivity

I chanced upon this 1D chain Mass Impurity model: At the end of all the derivations, it concludes that Case 1: $ 0 < M_0 < M$ The impurity is lighter than the host atoms. The frequencies ...
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35 views

What is a marginal fermi liquid in a nutshell?

I would like to know what are the main differences between the normal Fermi liquid theory and a marginal fermi liquid theory. What kind of systems can be described by the marginal liquid theory? What ...
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1answer
66 views

Boundaries in superconductors

In quantum mechanics we have the famous example of a particle in a box. The finite size of the System leads to a quantization of the momentum of the particle due to the Formation of standing waves in ...
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43 views

Tight-binding model parameters fitting from ab-initio calculation results

Or the problem can be rephrased as: How to extract the tight-binding parameters from first principle calculations? I have searched some articles but all of them just give vague descriptions when ...
5
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2answers
62 views

What do we know about the strength of the electron-phonon coupling in high-temperature superconductors?

I would like to clarify the situation of the electron-phonon coupling in high-temperature superconductors (or considering only the cuprates). The main question is what do we know about the strength of ...
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23 views

Effect of Phonon Density change

I am trying to figure out the phonon density change effect on anharmonic decay of phonons. How this two phenomena could be related and what could be the possible effect in such case. Moreover ...
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65 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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1answer
32 views

How can wavefunction degeneracy be incoperated into a tight binding model?

Say one wanted to calculate the band structure of the E2u orbital in some molecular crystal, which is the HOMO. How are the two states dealt with in the tight binding hamiltonian?
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59 views

Second law of thermodynamics in linear response theory

I am wondering about the appearance of irreversibility in the response functions or equivalently the correlation functions in a statistical mechanics system. The main principle that I have seen where ...
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26 views

MFT Approximation for Dilute Bose Gas

The Dilute Bose Gas has quartic Hamiltonian $$H=\sum_{k}\epsilon_k b_k^\dagger b_k+u\sum_{k\,k'q}b_{k+q}^\dagger b_{k'-q}^\dagger b_kb_{k'}.$$ It is said in a reference that Since the lowest ...