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

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Good place/supervisor for PhD in Theory of Condensed matter [closed]

I am currently finishing my undegraduate degree in physics and would like to do PhD in Theory of Condensed Matter field. Could you give advice on which are good groups/supervisors in the field. ...
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113 views

Topological quantum computation : Anyon model

Could someone tell me about Frobenius-Schur indicator and the associated cups and caps notation in context of anyon model. One possible reference could be Parsa Bonderson thesis which is freely ...
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208 views

Peierls Argument for Absence of Long Range Order

I'm really confused about the argument in Cardy's book for why there can't be long range order in 1D for discrete models. Let me just copy it out, and hopefully someone can explain it to me. He ...
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315 views

Higgs vs phonons

Jim Baggott's "Higgs" quotes David Millers' prize-winning one-page explanation of the Higgs mechanism (the one that evokes Margaret Thatcher crossing a room). I've heard that part many times, but not ...
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3answers
123 views

Should a polyatomic crystal behave similarly to the bulk of each/either of its constituent elements?

Generally, metals are usually fairly conductive, but their oxides aren't. I know conductivity is just one attribute, but in general, should you expect a, say, diatomic bulk crystal's properties to be ...
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2answers
252 views

Difference between charge density wave and charge distribution

We can always see modulated charge density, the Friedel Oscillation, around an probe charge due to other electrons' response. Can this be called charge density wave (I believe not)? If not, what is ...
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76 views

Compressibility and specific heat: interconnectedness and independence?

Consider a Mott insulator (insulator arising from strong correlations). This is an incompressible phase i.e. it costs energy to add a single particle to it; the ease of compression (compressibility) ...
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116 views

From Berry's phase to artificial Gauge potential

How a nonzero geometric phase in a loop is used to generate artificial gauge potentials? If possible, can you also tell how to generate the non-abelian artificial gauge potentials.
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67 views

Cellular structure in solid phase detonations

For gaseous and liquid detonations, the detonation propagates by the energy released at the triple-points which form a cellular structure. This structure is traced using a soot foil during ...
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199 views

Hollow gold bar

A scammer got a hollow gold bar and fills it with a combination of lead and air, with the same average density as gold. What's the simplest way of discovering the fraud? I know that x-rays will see ...
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1answer
140 views

Topological quantum computation: abelian vs. non-abelian anyons

We need non-abelian fractional hall states because of the ground state degeneracy http://rmp.aps.org/abstract/RMP/v80/i3/p1083_1 (arXiv version for free). But we can also have degeneracy even in case ...
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1answer
70 views

Meaning of the 'deep lattice limit' and 'shallow lattice limit'?

In condensed matter literature, at many places, the phrase 'deep lattice limit' is used. Please tell what is the deep lattice limit and the shallow lattice limit?
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1answer
415 views

valence bands in graphene

In Graphene, each carbon use 3 electrons to form sp2 bonding with neighboring, and in a unit cell, there are 2 carbon atoms, so at least these 6 electrons contribute to 6 valence bands. Then my ...
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66 views

What is the physical property of metal nanoparticles?

I am a Math student but now I have to deal with gold nanoparticles in aqueous solution. Now I was wondering whether the physical properties of gold nanoparticles are the same as the properties of gold ...
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1k views

What is Si-delta doping? [closed]

I want to know what the delta means in this case. I know the Si means the element used, by some way to doping. I guess the delta means that using some elements to create holes in semiconductor made ...
4
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1answer
149 views

Do indirect optical transitions “cool” the material a little?

So I'm reading in Ashcroft and Mermin about indirect optical transitions: So, a photon comes in, and it only excites the electron across the indirect band gap if a phonon with the appropriate wave ...
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81 views

The boundary between polycrystalline and crystalline

My current understanding of solid crystalline-like materials (please correct me if I'm wrong!) is that it is a continuum in terms of crystallinity, from amorphous (basically no periodicity) to single ...
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1answer
124 views

Can anyons emerge from momentum-space other than spatial dimensions?

So far in condensed matter physics, I only know anyons(abelian or nonabelian) can emerge as quasiparticles in 2D real-space. But is there any possibility to construct anyons in momentum-space ? And ...
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1answer
2k views

About Dirac cones

This nice image of Dirac cones (from this article), in a ($E,\vec k$ graph) will be an introduction for several questions, in the realm of topological insulators. 1) Does the Dirac cone appears ...
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1answer
749 views

Bound states and scattering length

What is the relationship between bound states and scattering length? What is the relationship between scattering states and scattering length? When we say, potential is 'like' repulsive for ...
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1answer
929 views

Experimental signature of topological superconductor

I was wondering if someone can provides some clear experimental signatures of a topological superconductors ? I was thinking about that, because for topological insulator, one of the hallmarks is ...
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1answer
187 views

Discretization of Hamiltonian using finite difference always justified?

I have this continuum version $$ H_{R}=\int dx\psi^{\dagger}(x)(\frac{p^{2}}{2}+V)\psi(x) $$ with $V$ as constant potential. Is it always justified to go from this to $$ \sum_{i}c_{i}^{ \dagger ...
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1k views

Reconciling topological insulators and topological order

We make an important distinction between the topological insulators (which are essentially uncorrelated band insulators, "with a twist") and topological order (which covers a variety of exotic ...
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1answer
262 views

Non-equilibrium Green functions

How do we use non-equilibrium Green's functions (NEGF) or the Keldysh formalism in the theory of quantum transport? Please take a simple example like the Hopping model with a non-equilibrium ...
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254 views

Kubo formalism application

Suppose I have some pertubative Hamiltonian on the Hubbard Hamiltonian and I want to calculate the change in current in linear response using the Kubo formalism. Now the kind of perturbative ...
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2answers
610 views

current operator in Hubbard model

How to derive the particle current operators for the non-interacting and interacting Hubbard model ? Hubbard Hamiltonian is given here with the interaction term: ...
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3answers
223 views

spectral function in condensed matter physics

What is the importance of deriving the results of perturbation theory in condensed matter physics in terms of spectral functions ?
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1answer
212 views

periodic boundary conditions for vortex in a square lattice

I am trying to follow this paper and track the dynamics of vortex motion on a discrete (square) lattice. The idea is to simulate the time evolution of the Gross-Pitaevskii (GP) equation, which reads ...
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2answers
500 views

Particle current operator in general vs Particle current operator for tight binding Hamiltonian

I am referring Mahan Many-Particle Physics. There are 2 particle current operators -one in general and one for the tight binding Hamiltonian. How do we go from the general current operator (1.195 in ...
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82 views

Types of Solitons

In the condensed matter literature, I have seen broadly two types of solitons which are dark and bright corresponding to fall and rise in density. (I know only the number density case ). But among the ...
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1answer
126 views

Why NPT ensemble is used for solid state phase transitions?

In Monte Carlo simulations of solid state phase transitions, why often Isobaric Isothermal ensemble (NPT) is used ? Why not NVT ? Here, N is number of atoms, P is pressure, T is temperature and V is ...
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168 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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1answer
69 views

Hexagonal Warping

Hexagonal warping had observed in $Bi_2Te_3$. Is it related somehow with the topological insulator type? Is it a characteristic of weak topological insulator or are there other reasons for this ...
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1answer
937 views

Trivial and Non-trivial topology of band structure

I don't understand the meaning of the expression "trivial topology" or "non-trivial topology" for an electronic band structure. Does anybody have a good explanation?
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1answer
681 views

Topological band structure, difference between a sphere and a donut

Kohmoto from TKNN(Thouless-Kohmoto-Nightingale-deNijs) who described the topology of the integer quantum hall effect always stressed the importance of the 2D Brillouin zone being a donut due to ...
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92 views

Phase diagram of SO(5) rotor model

It was originally a problem from Professor Eugene Demler's problem set. Consider an SO(5) rotor model: \begin{align}\mathcal{H}=\frac{1}{\chi} ...
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1answer
117 views

An approachable example of a field with a “mass gap”

Preamble: I have come to believe that alot of difficulties in explaining physics to people of all levels comes from the relatively mundane idea of a wave equation with a mass gap $$\left(-\partial^2_t ...
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2answers
367 views

Quantum to classical mapping: quantum criticality and path integral Monte Carlo

I'm trying to understand the connections between quantum models in d dimensions and classical models in (d+1) dimensions within two, possibly related, contexts: (i) in path integral monte carlo, the ...
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2answers
463 views

Why is the Fermi surface stable?

As a condensed matter physicist, I take it for granted that a Fermi surface is stable. But it is stable with respect to what? For instance, Cooper pairing is known as an instability of the Fermi ...
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1answer
153 views

How to justify matter-field interaction for non-gauge-invariant Hamiltonian?

I'm wondering how can one formally justify the electromagnetic response of a system which does not verify local U(1) gauge invariance. A good example of what I would like to consider is given by the ...
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1answer
152 views

Accelerated charged particles produce electromagnetic radiation, but holes (the charge carriers) do not. Is this correct?

Holes are treated as particles in solid-state physics, so I've had some trouble with reasoning through this properly.
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106 views

About the microscopic form of magnetocrystalline anisotropy

Currently people write magnetocrystalline anisotropy as $H_{an}=-K s_x^2$ from its classical counterpart: $H_{an}=-K ( \sin \theta)^2$ where $K$ is the anisotropy constant, but for spin 1/2, $s_x^2$ ...
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2answers
361 views

Imposing anti-commutation relations on fermionic quasi-particles

In many theories of CMT, we assume the nature of quasi-particles (without giving proper justifications). For example, we assume nature of quasi-particles to be fermionic in case of a interacting ...
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1answer
283 views

The critical point of Bose-Hubbard model

The Hamiltonian of Bose-Hubbard model reads as $$H=-t\sum\limits_{<i,j>}b_i^{\dagger}b_j+h.c.+\frac{U}{2}\sum\limits_{i}n_i(n_i-1)-\mu\sum\limits_in_i$$. In the limit $t\ll U$, the ground ...
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360 views

Toward the establishment of non-equilibrium (quasi-equilibrium) magnon BEC theory

In 2006, Demokritov et al have reported that they have achieved the observation of quasi-equilibrium magnon Bose-Einstein condensation (BEC) in YIG at finite (room) temperature by using the method ...
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1answer
105 views

penetration of a solid body in a liquid

A solid (for example a steel ball) is moving with a certain constant velocity U toward a liquid in a container; I can write the equations of motion of the solid when it has a little part of it in the ...
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1answer
214 views

The relation between spectral function and band structure

I am confused by the wavevector in spectral function A(k,w). How to understand this k for a periodic structure? And how is it related to the k (in first Brillouin Zone) we use in the band structure? ...
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2answers
618 views

Differences between spin waves and spin density waves

Roughly speaking, in condensed matter systems, spin waves and spin density waves are both low-energy states with spin that varies spatially. What precisely are their differences?
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2answers
868 views

How does a phonon cause two electrons to attract each other and form a cooper pair?

We know that like charges repel each other. But my professor claimed that two electrons can attract each other as well. What he said was that due to screening an electron travelling at some speed ...
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235 views

How to cut a stone on on a White Dwarf

I've heard that white dwarfs are extremely dense and hard. So, if I had a piece of white dwarf matter, would it be possible to cut it (or otherwise) into a custom shape? How could one do that?