Questions tagged [condensed-matter]

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

Filter by
Sorted by
Tagged with
0
votes
0answers
26 views

Strain field and periodic boundary conditions

Let's say I have a lattice, and I impose periodic boundary conditions. I want to construct a tight-binding model on a strained lattice, and I can determine the change in the hopping parameter based on ...
3
votes
1answer
68 views

What is topological material?

Recently, topological material has been a hot topic in condensed matter physics, but I don't know what is topological material and how to distinguish topological material from band diagram. And how ...
5
votes
1answer
131 views

Question about the retarded Green's function and the analytic continuation of the Matsubara Green's function

This question is a little bit mathematical. It is about the relation between correlation function in the Matsubara frequency and the retarded correlation function in the real frequency. The following ...
8
votes
2answers
134 views

If matter comes from energy, does this mean that energy has weight?

If the matter in the Universe formed from the energy of the Big Bang, and matter has weight, does this mean that energy has weight? Moreover, as the Universe expands over time, does its overall ...
1
vote
0answers
42 views

Lattice hopping at boundary in graphene lattice with magnetic field

Let's say I have a tight binding model for graphene, where I have a two-atom basis and three nearest neighbor vectors. I've applied a homogenous magnetic field $B$ in the z-axis, and can take the ...
0
votes
0answers
35 views

What is the density of states $SiO_2$?

We build the model by the finite element method. In our model here is silicon dioxide (SiO2). To carry out calculations, it is necessary to know the density of states and the effective mass. Question:...
1
vote
1answer
45 views

Under which condition the drift velocity stops increasing proportionally with respect to the electric field

Our professor asked us a question the other day but i wasn't able to figure it out. If we increasing Electric field then drift velocity will increase, Because of this Equation: Vd = μ * E But at ...
1
vote
1answer
38 views

Symmetry arguments on the Berry connection and the polarization charge

Consider the Berry connection $$ A_n(\mathbf{k})=i \langle n(\mathbf{k})|\nabla_{\mathbf{k}}|n(\mathbf{k})\rangle $$ and the polarization charge $$ \mathbf{P}=-\frac{1}{4\pi^2} \int_\mathrm{B.Z.}\...
1
vote
0answers
22 views

Conserved charge during renormalization-group flow

Let us consider a quantum system (at zero temperature) with a continuous (anomaly-free) symmetry $G$ and there exists a corresponding conserved charge $Q$. Then we perturb this (might-be critical) ...
0
votes
0answers
65 views

Why the correlation function of 2D classical XY model is written so?

2D classical XY model $$H = -J\cos(\theta_{i}-\theta_{j})%$$ is famous for Berezinskii-Kosterlitz-Thouless phase transition. This is because of the difference of correlation function between hot and ...
0
votes
0answers
22 views

What is the analog of quantifiable magnetic field in condensed matter systems?

What is the analog of the magnetic flux density B, which is an observable and quantifiable quantity (i.e. $|B|$ can be defined in Teslas), in the anomalous QHE? For instance in the Haldane model? In ...
0
votes
1answer
33 views

Fermi gases and holes

It is a well known fact that at $T\to0$ the energy of the Fermi level for a noninteracting electron gas is given by $$E_{F}=\frac{\hbar^{2}k_{F}^{2}}{2m},\,\,k_{F}=(3\pi^{2}n)^{1/3},$$ where $k_{F}$ ...
0
votes
1answer
57 views

Help integrating potential of interaction

I'm having trouble integrating a potential that is very present in many theories regarding Condensed Matter Physics. The potential I'm trying to integrate is $$\int_{0}^{\alpha}d^3\textbf{r}\frac{1}{|\...
1
vote
0answers
16 views

In spin systems, a mean field with nonzero Chern number after Gutzwiller projection changed into trivial state?

The mean field is nontrivial because of nonzero Chern number. The gauge symmetry is Z2. Under Gutzwiller projection, I calculate the ground state degeneracy(GSD) and find that the GSD is one(trivial ...
0
votes
0answers
10 views

Physical interpretation of Bogolyubov sound with zero momentum in BEC

The point with zero momentum in the spectrum of acoustic phonon corresponds to a translation of the crystal. Is there an interpretation like this of the Bogolyubov sound in BEC? I have read that in ...
1
vote
0answers
103 views

Density of states for a tight binding model

So we have been given a dispersion relation of the form: $$ E=6-2(\cos k_xa+\cos k_ya) $$ and asked to calculate the density of states. The equation for the density of states is (eq 2.48 from here ...
3
votes
0answers
52 views

Collective modes of charge density wave

The question is about collective modes of charge density waves, i.e., amplitude and phase fluctuations $\delta,\phi$ of the order parameter $\Delta(x,t)=(\Delta_0+\delta)e^{i\phi}$. I read on p.1 of ...
0
votes
2answers
35 views

Is the DOS (density of states) wrong for degenerated case?

The density of states (DOS) is defined as $$\mathcal{N}\left(\lambda\right)=\sum_{n=1}^{M}\delta\left(\lambda-\lambda_{n}\right).$$ We can then get $$\int d\lambda\mathcal{N}\left(\lambda\right)=M,$$ ...
1
vote
0answers
141 views

Feynman diagrams: from QFT to condensed matter

I studied Feynman diagrams in quantum field theories and I'm going to study them in the context of condensed matter physics. In this post Books for Condensed Matter after Ashcroft/Mermin, two books ...
0
votes
0answers
57 views

How to interpret Berry curvature in 2-band model?

While studying the 2-band Haldane model, I realized that I am missing an intuitive picture of how Berry curvature comes into play, especially when considering an adiabatic loop. A 2-band model has 2 ...
0
votes
0answers
24 views

Landau level in particular cases

If we consider an array of identical uncoupled spinless non-interacting one-dimensional wires, as shown in Fig.(a) with a single-particle electronic dispersion E(k), which we can take to be parabolic ...
8
votes
1answer
105 views

Why is the density of a BEC so low?

I've just begun reading C. Pethick and H. Smith's textbook "Bose-Einstein condensation in dilute gases" (Cam. Uni. Press). In the Introduction, they contrast the density of atoms at the centre of a ...
2
votes
2answers
86 views

How can I simulate a ground state degenerate system numerically?

I'm using numerical method like DMRG to simulate ground state of correlated systems. But the degeneracy of the ground state has long bothered me: When degeneracy exists the ground state isn't unique. ...
1
vote
0answers
34 views

How can I compute the spin texture for a $SU(2)$ gauge model?

I am trying to determine the helicity of 4 Dirac cones in my model, and one way I want to approach it is by plotting the spin-texture. However, I am unsure of how one would calculate the spin-texture ...
2
votes
1answer
42 views

Behaviour of quantum spins

I am reading the Jordan-Wigner transformation in the book "Introduction to many-body physics" by Piers Coleman. When I read the introduction of this chapter, it is stated that: Quantum spins are ...
3
votes
1answer
176 views

What is the atomic limit?

I am attempting to grasp topological superconductivity for an assignment and in trying to understand what makes a quantum system topological have came across the following paragraph; "In the case ...
1
vote
1answer
204 views

What is the charge neutrality point in solid state physics?

I came across the term in solid state physics recently, usually in the context of a gate voltage applied to some solid in order to tune the charge carrier density. What is the definition of the ...
0
votes
1answer
44 views

What creates a negative charge in the material?

What creates a negative charge in the material? Is it an electron or a holon? Holons as I understand is a math. But what then creates an electrostatic repulsion? Is it still electron?
0
votes
1answer
46 views

Wigner Seitz cell

While searching the difference between primitive cell and unit cell I have seen that "Primitive unit cells contain only one lattice point, which is made up from the lattice points at each of the ...
1
vote
0answers
53 views

What is the standard definition of quantum spontaneous symmetry breaking?

i found many answers about spontaneous symmetry breaking here but i am not sure to see what is the standard definition of SSB. i am interested in the BCS theory and i would like to know how the ...
0
votes
1answer
89 views

Momentum Space Representation of the Tight Binding Hamiltonian

I am trying to represent the tight-binding Hamiltonian \begin{equation} \hat{H}_{TB} = \sum_{\sigma} \sum_{\alpha,\beta} \sum_{\mathbf{R}_1,\mathbf{R}_2} t^{\alpha,\beta}_{\mathbf{R}_1,\mathbf{R}_2} \...
0
votes
1answer
56 views

To get short-range interaction from long-range interaction

Interactions in Condensed matter systems are almost exclusively the electromagnetic interactions which are long-range. But it often gives rise to short-range interactions in systems e.g., exchange ...
0
votes
1answer
37 views

Does pseudospin necessarily carry angular momentum?

And if so, why? I was told that anything that mathematically transforms like a spin must carry angular momentum. Is this true? One example of pseudospin is electrons in graphene on the A and B ...
1
vote
1answer
100 views

$sp^3$ Hybridization wavefunctions and probability density

I have plotted a hydrogen-like sp3-hybrid orbital probability density and it looks like this: I can plot 4 overlapping probability densities in a tetrahedral shape: So far it looks OK. But when I'm ...
4
votes
1answer
56 views

What is line broadening phenomenon in quantum many body physics?

I have been reading Anderson's paper, "Absence of diffusion in a certain Random Lattice" and found the concept of inhomogeneous broadening. I couldn't really find a satisfactory explanation with a ...
2
votes
0answers
84 views

How does Bohmian Mechanics explain superconductivity?

I'm looking for sources that discuss how Bohmian Mechanics explains superconductivity. Are there still Cooper pairs? Phonons? I saw one vague reference to vortices, but no details. This is my first ...
0
votes
0answers
30 views

Can the total energy of a solid be measured with photoemission?

Angle resolved photoemission spectroscopy (ARPES) is a really popular tool developed to study the behavior of solids by looking at the behavior of their photorlectrons. This is used to measure ...
2
votes
1answer
52 views

Where is the missing energy in the Debye-Waller effect?

X-ray/neutron scattering from crystals and liquids is well-described by the scattering theory to give the (dynamic) structure factor which is a function of momentum and energy: $$S(\mathbf{k},\omega)=...
1
vote
0answers
45 views

How to interpret overlap in Hamiltonian if it is not a degeneracy?

In Fruchart et al.'s An Introduction to Topological Insulators, the Bloch Hamiltonian for a two-band insulator is given in the general form $ H(k)= $ \begin{bmatrix} h_0+h_z & h_x-i h_y \\ ...
1
vote
1answer
56 views

Do topological transitions only occur at Dirac points?

Topological phase transitions happen when the band gap closes. It is not true that all band crossings are topological. There are Dirac (linear) band crossings, quadratic band crossings, Dirac-like ...
0
votes
0answers
7 views

second-harmonic generation and inversion centers confined to a planar defect

Let's say that we have a phase which breaks inversion symmetry. Now lets say two domains of this phase meet at a plane such that the whole system now has inversion symmetry, with the inversion ...
2
votes
1answer
48 views

Is there a simple way to numerically solve interacting fermion systems like for spins?

I know that if one has a spin chain of N spins, with the interaction described by some Hamiltonian, one can find the eigenstates and energies by using Kronecker products to write the Hamiltonian as a $...
3
votes
0answers
66 views

Fermionizing the Gell-Mann Algebra

In condensed matter physics one often solves a spin Hamiltonian by transcribing the Pauli matrices into fermionic operators. For instance, in the Kitaev model you can introduce four Majorana modes for ...
2
votes
0answers
34 views

Why are there two magnon propagators in Ferromagnetic system?

I am confused that the authors of ref.[1,2] defined two magnon propagators in the ferromagnetic system with magnon-phonon coupling (which is similar to electron-phonon coupling). They defined ...
0
votes
0answers
53 views

Identity when Diagonalising Single-Particle Hamiltonian

Sorry the title is not precise; wasn't sure how to make it so (this is perhaps a straightforward question). The following is an identity I see quite often when reading lecture notes about ...
0
votes
0answers
52 views

Is the SSH model a tight binding model?

Sorry if this is an obvious question. I have trouble understanding where the Hamiltonian of the Su-Schrieffer-Heeger model comes from? May I confirm if it is from the Tight Binding Model? The creation ...
2
votes
1answer
114 views

Why can AdS/CFT correspondence be applied to condensed matter systems when their space is not anti-deSitter?

The AdS/CFT correspondence postulates a duality between string theory of gravity and a CFT on an AdS background. This duality is employed in some condensed matter systems. I was wondering why it is ...
0
votes
1answer
34 views

Using FFT for spins in a non-cubic crystal lattice

Classical Ising/XY/Heisenberg models on a crystal lattice are commonly used to model magnetic materials. These can be studied using Monte Carlo simulations on a computer. Magnetic systems are often ...
1
vote
1answer
1k views

Why is a liquid nitrogen canister not cold on the outside when inside the temp of the sealed liquid is -320F? [closed]

...or IS the inside temperature ambient temperature? Surely the insulation of the container is not sufficient to seal in that cold? I.e. if you had an unsealed bowl of liquid nitrogen with the same ...
2
votes
0answers
48 views

Energy bands. Bonding and antibonding orbitals

In tight-binding wikipedia article it is said that bonding and anti-bonding orbitals correspond to different $k$-values in a single energy band. At the same time in Cordona Fundamentals of ...