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

learn more… | top users | synonyms

4
votes
4answers
211 views

If you suddenly move a piece of metal, will that disturb the free electron density?

If we have a hollow pipe sitting at rest filled with gas and we moved the pipe suddenly along its length to the right, then the gas density will be momentarily higher near the rear of the pipe and ...
2
votes
2answers
185 views

A conceptual question about Green's function's treatment of interaction

Here we have electron gas and some other stuff. We expand the Hamiltonian to the 1st order of one single harmonic oscillator's displacement $\vec{u}$. Its equilibrium position is at the origin. Then ...
2
votes
1answer
89 views

Bravais lattice with sublattices : why multiple bands?

I have a very naive question : given a tight-binding model (with nearest-neighbor hoping) on a lattice defined by a Bravais lattice with a number of sublattices (for instance the honeycomb lattice is ...
0
votes
2answers
81 views

Is crystal momentum an operator?

My teacher has for Bloch waves the notation $\langle \vec{r}|\vec{k} \rangle = e^{i\vec{k}\cdot \vec{r}}u_{\vec{k}}(r)$ and uses it consistently. However, does this not assume that there is an ...
2
votes
0answers
45 views

Qubit in Type 1.5 superconductor?

I'm interested in Type 1.5 superconductors, first proposed by Egor Babaev in 2002 and found in the laboratory in 2009 (magnesium dibromide). Such conductors favor small bundles of vortices. The most ...
4
votes
0answers
166 views

Finding the ground state of the toric code Hamiltonian

How do I write by proof, the ground state of the toric code (by Kitaev) Hamiltonian $ H=-\sum_{v}A(v)-\sum_{p}B(p) $ where $A(v)=\sigma_{v,1}^{x}\sigma_{v,2}^{x}\sigma_{v,3}^{x}\sigma_{v,4}^{x}$ and ...
0
votes
0answers
28 views

Is there a generic term for orbital groups such as $e_g$ and $t_{2g}$?

I am looking for a generic term for sets of atomic orbitals (viz. spherical harmonics) which are grouped by crystal symmetry. The most familiar examples would be $e_g$ and $t_{2g}$ (in cubic ...
1
vote
0answers
32 views

Simple examples for exchange and correlation

Is there an easy, in the best case intuitive, explanation of the difference of exchange and correlation? Is there a simple way to distinguish whether a certain contribution is due to exchange or ...
4
votes
0answers
114 views

Confusion regarding field operators

Second quantisation of the scalar field leads to an algebra of quantum field operators $$ [\phi(x),\phi(y)] = 0, \ \ [\pi(x), \pi(y)] = 0, \ \ [\phi(x),\pi(y)] = i\hbar \delta(x-y). $$ Where the field ...
0
votes
0answers
112 views

Fermi Energy Variation

What would be a good Internet link that would properly explain Fermi Energy? How does the Fermi Energy of a material vary with external influence, such as doping of the material, and applied ...
1
vote
0answers
174 views

How do I write the Hamiltonian for a 3-level system?

I came across following types of three-level systems like V-system, Λ-system and 2-photon absorption It seems that their Hamiltonians can be written intuitively by checking out the coupled levels ...
10
votes
1answer
583 views

Do we have magnetic monopole? Is charge, according to yesterdays paper on Nature by Ray-Roukokoski-Kandel-Möttönen-Hall (30.01.14) quantized?

As everybody here knows, Maxwell's equation would look more beautiful if a magnetig charge were present. Beyond the aesthetics question, if a single magnetic Dirac monopole would be found, the ...
3
votes
1answer
128 views

Do holes have wavefunctions?

Do holes (as in the absence of an electron) have wavefunctions? In my understanding, when we talk about holes, we are implicitly invoking two multiparticle wavefunctions: $$\tag{1} \Psi(x_1,...,x_N)= ...
3
votes
1answer
134 views

Group analysis forbids band-crossing in 1D?

Group analysis forbids band-crossing in 1D in terms of conventional band theory. I read this in a good solid state physics book. But there's no explanation at all. Can anyone help on this?
0
votes
0answers
48 views

Diffusion coefficient of a crystal

I've been trying to work this out so I can give a hand waving argument for one of the effects I'm observing on the fly and I find myself going down a rabbit hole that seems way too complicated for ...
5
votes
1answer
302 views

Interpretation of the 1D transverve field Ising model vacuum state in a spin-language

The 1D transverse field Ising model, \begin{equation} H=-J\sum_{i}\sigma_i^z\sigma_{i+1}^z-h\sum_{i}\sigma^x_i, \end{equation} can be solved via the Jordan-Wigner (JW) transformation (for further ...
1
vote
1answer
115 views

Coupling of open and closed channels in Feshbach resonance model

Feshbach resonance is described with coupling of 2 systems differing in the form of potentials :- one is said to produce a bound state (in 'closed' channel) and other is to produce scattering states ...
1
vote
1answer
44 views

Experimental methods for finding London penetration depth

I have been doing some readings on superconductivity and have come across the London penetration depth. I somewhat understand how it comes into play with the London equation and Ampère's law. Right ...
4
votes
3answers
142 views

Why can we quantize macro(meso)scopic harmonic oscillator?

It is well known that we have got many kinds of quantized macro(meso)scopic harmonic oscillators or so in tiny mechanical systems. People are talking about cavity cooling and so on. However, it is ...
3
votes
1answer
222 views

Berry curvature of Landau levels

If we consider an electron on a two dimensional surface with a magnetic field normal to the surface, we know the states the electron can occupy are Landau levels. If we additionally impose periodic ...
3
votes
1answer
753 views

s-wave, p-wave or d-wave collisions in scattering theory

In scattering theory, what is a good intuitive picture to think of s-wave, p-wave or d-wave collisions ? What is their importance and what are the examples where a particular one is assumed to be the ...
2
votes
1answer
72 views

Triangular lattice arrangement of vortices in a superfluid

In a simply connected container containing a superfluid and rotating, there is a net circulation of superfluid. This is found due to the vortices formed, around which the superfluid rotates. These ...
1
vote
0answers
49 views

Falling to closest quantized circulation level in a rotating superfluid

To make a superfluid rotate in an annulus shaped container, we start with a normal fluid, rotate the container, then cool it to below critical temperature to get a rotating superfluid. The allowed ...
3
votes
0answers
141 views

Does the projected spin state of the $d+id$ mean-field Hamiltonian on a triangular lattice has time-reversal(TR) symmetry?

Consider the following $d+id$ mean-field Hamiltonian for a spin-1/2 model on a triangular lattice $$H=\sum_{<ij>}(\psi_i^\dagger\chi_{ij}\psi_j+H.c.)$$, with $\chi_{ij}=\begin{pmatrix} 0 & ...
3
votes
1answer
128 views

Chiral Spin Liquid(CSL), Chern number, and the ground state degeneracy(GSD)

Consider a 2D gapped CSL with a nonzero Chern number $m$, then is the GSD of the system on a torus directly related to the Chern number $m$? For example, see this article, in the last paragraph on ...
1
vote
2answers
329 views

What is the difference between diamagnetism and superconductivity?

Basically, What is the difference diamagnetism and superconductivity? As far as I understand, diamagnetism comes from the fact, that all electrons in a solid, when exerted by an external magnetic ...
2
votes
0answers
146 views

How is Laughlin's gauge argument explaining integer quantum hall effect(IQHE)?

It seems essential in Laughlin's gauge argument that the sample has to be cylindrical(or with similar toplogy), so that we can "thread" a thin solenoid through to control the gauge function on the ...
1
vote
1answer
163 views

Why does a bucket of Water weigh more than a bucket of Air?

Given the numerous chemical compounds found in dry air [compressed into a liquid] of a given volume [lets say $22.4$ L for simplicities sake] whose atomic weights far surpass that of water alone ...
1
vote
2answers
109 views

Phonon mode in canonical and grand canonical ensemble

I derived the averaged energy for phonon mode with frequency $\omega$ in canonical ensemble and in grand canonical ensemble. Averaged energy derived in canonical ensemble is ...
0
votes
1answer
271 views

Overview and doubts about Bloch's theorem and the concept of partial density of states

So I have a large confusion with QM as applied to solid state. The following is a summary of what I know, what I think I know, and what I know I don't know. I hope to stir a discussion that will help ...
0
votes
2answers
109 views

Compute distance between planes in a crystal

I want to compute the distance between two (111) planes in a cubic crystalline structure, in order to do some computations involving Bragg reflection. I have a sketch of which the (111) planes are, ...
0
votes
1answer
65 views

Magnetic field exclusion and retention in superconductors

I'm studying the behaviour of superconductors in different cases, and I can't understand this. We have a superconducting cylinder with a coaxial hole inside (vacuum). When the cylinder is cooled ...
1
vote
1answer
319 views

Generalized tight-binding model - how to solve it?

Consider a generalized 1D tight-binding model (without spin) with the following Hamiltonian \begin{equation} \mathcal{H}\left(\{\chi_{r,r+1}\}\right)=\sum_{r}(\chi_{r,r+1}c^\dagger_rc_{r+1}+h.c.)~, ...
1
vote
0answers
49 views

Which quantum models violate the third law of thermodynamics and have an ergodic ground state?

Which any condensed matter quantum spin models over a finite lattice of size N which violates the third law of thermodynamics with ergodic mixings for the ground state?
1
vote
1answer
80 views

How is domain wall formation related to spontaneous symmetry breaking?

It is said that domain wall formation is the signature of in spontaneous symmetry breaking but not explicit symmetry breaking. Why is this so?
-1
votes
1answer
1k views

Partition function for a microcanonical ensemble

Is it possible to write down a partition function for a microcanonical ensemble?
1
vote
0answers
52 views

Electron-electron interaction in solids

We always consider a Coulomb interactions between electrons in the Hamiltonian to modelize a solid. Why not to take into account retardation effects of the electromagnetic interaction which go beyond ...
1
vote
1answer
103 views

Phonon-phonon-interaction as higher order terms in the potential

Is there a simple way to understand why phonon-phonon-interaction is described by higher order terms in the potential? I mean: Having a quadratic potential is essential for the definition of the ...
1
vote
1answer
51 views

How do you justify neglecting electron-electron interaction in the Drude model?

I'm sure there's some way to justify it. Maybe a screening effect?
2
votes
0answers
95 views

Does Fluctuation-exchange (FLEX) approximation including spin-orbit coupling (SOC) exist?

FLEX method was invented by N.E.Bickers and D.J.Scalapino in 1989 (PRL 62,961; Ann. Phys. 193,206). Later it was extended to multi-orbital system (T.Takimoto,PRB,69,104504). But I don't find FLEX ...
0
votes
0answers
13 views

Form factor and Guinier regime [duplicate]

sorry for reposting. I dont get why it is such a good idea to plot the logarithm of the form factor vs $Q^2$ in Guinier plots. It seems arbitrary to me.
0
votes
1answer
98 views

Guinier regime for form factor

Why is it such a good idea to plot the logarithm of the form factor vs $Q^2$ in Guinier plots. It seems arbitrary to me.
1
vote
2answers
126 views

Moving Between Degenerate Vacua?

In spontaneous symmetry breaking, moving round the circular valley of Mexican hat potential doesn’t cost energy. These angular excitations are called Goldstone bosons. But doesn't the angular ...
3
votes
1answer
73 views

Development/history of Mesoscopic Physics/quantum transport

I am studying mesoscopic physics/quantum transport. Now I am wondering (out of interest): how did this field emerge and what made it such a huge field? I couldn't find this somewhere clear on the web ...
4
votes
1answer
178 views

Entanglement entropy of 1D chiral Fermion

I was told that the entanglement entropy $S_E$ on the ground state of a (1+1)D conformal field theory (CFT) follows the logarithmic behavior $S_E=\frac{c}{12}\ln L$ where $L$ is the length scale ...
3
votes
1answer
243 views

Is the spin-rotation symmetry of Kitaev model $D_2$ or $Q_8$?

It is known that the Kitaev Hamiltonian and its spin-liquid ground state both break the $SU(2)$ spin-rotation symmetry. So what's the spin-rotation-symmetry group for the Kitaev model? It's obvious ...
2
votes
1answer
224 views

Edge states in the “half BHZ” model

Consider the "half BHZ" Hamiltonian $${\cal H}=\sum_{\mathbf{k}}\left(A\sin(k_{x})\sigma_{x}+A\sin(k_{y})\sigma_{y}+{\cal M}(\mathbf{k})\sigma_{z}\right)c_{\mathbf{k}}^{\dagger}c_{\mathbf{k}}$$ where ...
0
votes
1answer
163 views

Do Cooper pairs act like Cheshire cats?

Could the pairing up of electrons be explained by their spin being in a different position? What would separating the spin from an electron in matter do in theory?
5
votes
1answer
107 views

Do we have a fundamental Hamiltonian for the system of H$_2$O molecules?

From the quantum mechanics(QM) viewpoint, does there exist a Hamiltonian $H$ for the system of H$_2$O molecules? Assume that the number of H$_2$O molecules is fixed. Imagine that by calculating the ...
5
votes
2answers
160 views

Is it possible to determine the universality class of phase transitions by just analysing symmetry?

Since phase transition is closely connected with symmetry, I am wondering whether it is possible to determine the universality class of phase transitions just by symmetry? Actually, I found it is ...