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

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1answer
266 views

Does the low-energy gauge structure depend on the choice of $SU(2)$ gauge freedom?

The starting point and notations used here are presented in Two puzzles on the Projective Symmetry Group(PSG)?. As we know, Invariant Gauge Group(IGG) is a normal subgroup of Projective Symmetry ...
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0answers
26 views

Open-source code for computing response functions

Summing Feynman diagrams to compute the response functions of a microscopic model is common in many areas of physics. While conceptually straightforward, the task can be computationally intensive. ...
2
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2answers
149 views

Is the photon truly not absorbed in Raman scattering?

In reading about Raman Scattering, I was thinking while reading it "okay, incident photo absorbed by molecule, molecule goes to higher energy vibrational state, molecule re-emits photon with either ...
11
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3answers
2k views

Is the speed of sound almost as high as the speed of light in neutron stars?

Have you ever wondered about the elastic properties of neutron stars? Such stars, being immensely dense, in which neutrons are bound together by the strong nuclear force on top of the strong gravity ...
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2answers
107 views

Logarithmic discretization in Anderson´s model

Is there some motivation for the construction of Ladder operator that compound the recursive halmitonian of the Anderson model for numerical renormalization contained is this paper?
6
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1answer
194 views

Why is $\textbf{D}$ the response to $\textbf{E}$?

In the text Wooten, equation 2.69 shows $\textbf{D}$ being the response to $\textbf{E}$ with $\epsilon$ as the response function: $$ \textbf{D}(\textbf{r},t) = \int d\textbf{r}^{\prime} \int ...
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0answers
22 views

How do phonons and spinwaves interact? [closed]

What governs the coupling of acoustic phonons to transverse and longitudinal spinwaves? Is there a simple picture?
3
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3answers
376 views

Distinguishable, Indistinguishable Paramagnetic Ideal Gas

In the canonical ensemble, the partition function for an ideal gas is given by: $$\frac{Z}{N!}$$ The factor $N!$ accounts for the indistinguishability of the particles of the ideal gas. What ...
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0answers
56 views

Simple Explanation of Kondo Effect

Does anyone have a simple explanation of the Kondo Effect? (i.e. a simple physical picture + maybe equations to think of?) My current understanding is this: If we consider an electron scattering ...
24
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4answers
5k views

Good reading on the Keldysh formalism

I'd like some suggestions for good reading materials on the Keldysh formalism in a condensed matter context. I'm familiar with the imaginary time, coherent state, and path integral formalisms, but ...
0
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1answer
22 views

How is the ground state of an insulator related to a confined state and a localized state?

For an insulator, the real part of the conductivity is zero, i.e., the imaginary part of the current-current correlation function is zero. How is this related to a confined state and a localized ...
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0answers
37 views

About the orthogonality catastrophe

I am reading the book of Mahan. In the section of orthogonality catastrophe, I can understand that the two N-particle Slater determinants ($\Phi_i$ and $\Phi_f$) are almost orthogonal as $N\rightarrow ...
3
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0answers
69 views

Superconducting Order Parameter and Time Reversal Symmetry

How to understand the following definition of a time reversal operation $K$ given in the review by Sigrist and Ueda: $$K a_{\mathbf{k},s}^{\dagger} = \sum_{s'} (-i\sigma_y)_{s,s'} a_{-\mathbf{k},s'}$$ ...
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2answers
191 views

Sum of Green's functions in condensed matter

I am working on the Ginzburg-Landau model for Charge density waves, and I am carrying out the sum of Green's functions to calculate the terms in the GL model. Is the sum's order over $ \vec{k} $ (or ...
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0answers
9 views

Connection bewteen annihlate a majorana zero mode and annihlate a single weyl point?

In these two cases, a single majorana zero mode can't be removed, neither does a single wely point. They must be removed in pairs. Is there any connection between these two facts?
0
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1answer
71 views

Tight binding Hamiltonian for 2D finite dimensional lattice and nanowire

The Hamiltonian of a 1D lattice having finite N atoms, (if we consider one basis per atom) is given by the following N by N matrix- Here 'E' is the onsite energy and 't' is the hopping integral. ...
4
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1answer
195 views

What kind of free energy do we use for a superconductor in a magnetic field?

My reasoning is as follows (using Gaussian units): Start from the second law: $$dU=TdS+dW,$$ where $dW$ is the work done by the magnetic field. To derive $dW$, we consider a solenoid with current ...
2
votes
1answer
230 views

Quasi-particle and quasi-hole excitations of Laughlin states and generalization of Laughlin states

The Laughlin wave function at filling fraction $\nu=\frac{1}{m}$ is \begin{equation} \Psi_m=\prod_{i<j}(z_i-z_j)^m e^{-\sum|z_i|^2/4l_B^2} \end{equation} It is claimed in section 7.2.3 of Wen's ...
5
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1answer
214 views

Phase Transition at Zero Temperature (Not QPT)

As is well known the Ising model exhibits a phase transition, except the one dimensional case in which the phase transition occurs strictly at $T=0$. Now I have always thought that this makes the case ...
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0answers
50 views

Green's functions and spectral function

I'm struggling to understand something in the book by Fetter & Walecka, p.295, relating to the causal ($G$), advanced ($G^A$) and retarded ($G^R$) Green's functions, and the spectral function ...
2
votes
0answers
14 views

Why do Heavy-Fermions primarily form in compounds containing f-electrons?

I'm trying to understand why the majority of Heavy-Fermions form in materials containing unpaired f-electrons (Ce, Yb, U being the most common), rather than in materials with unpaired d-electrons (In ...
3
votes
1answer
34 views

Conservation of Angular Momentum in Einstein - de Haas effect

I am not really sure why the law of conservation of angular momentum should hold true in the Einstein - de Haas effect. Consider the following excerpt about the phenomenon (taken from Magnetism in ...
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0answers
24 views

The question about codimension of fixed point and about irrelevant operators

Recently I've read about Wilsonian renormalization group (WRG) in context of condensed matter phase transitions. The important concepts of WRG are fixed points and type of operators (eigenvalue, ...
0
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1answer
222 views

Tight binding in the limit of large system size

Suppose that one has a continuous Hamiltonian with spin-orbit interaction, for example $H=-\dfrac{\mathbf{p}^2}{2m} +\kappa({\boldsymbol\sigma}\times\mathbf{p}) + U(x)$ and want to approximate this ...
2
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1answer
572 views

Phonon Momentum

I am reading Charles Kittel's solid state physics and wondering what's the mechanism that neutron waves and photons can interact with phonons and the process obey the generalized momentum-energy ...
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0answers
26 views

How to construct the matrix of Hamiltonians for a hexagonal lattice

For part of a project I need to solve the TISE, HΨ=ESΨ (where H is the matrix with elements <Ψi|H|Ψj>, and S is a matrix with elements <Ψi|Ψj>) for different lattices. I've done this for a ...
3
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1answer
244 views

Hartree-Fock correction to $e$-$e$ interaction

The corrections to the energy per electron in a jellium model (uniform distribution of positive ion charge approximation to the regulated long range order ionic array) is given by (in units of Ry) ...
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0answers
20 views

About dispersion relation for three different energy bands

I am trying to solve a dispersion relation by solving a 3X3 determinant. But this cubic equation gives me complex energy. Does complex energy make sense in condensed matter physics? I don't know what ...
1
vote
1answer
564 views

Peierls substitution vs minimal coupling

In the presence of vector potential (let's assume it's uniform), a tight-binding Hamiltonian will be changed according to the Peierls substitution: $$t_{ij}c_i^{\dagger}c_j \to ...
2
votes
1answer
220 views

Green's function for 1 D hubbard model?

Consider the 1D two-site Hubbard model at half filling $H=-t\sum _{\sigma} (c_{1\sigma} ^{\dagger}c_{2\sigma}+h.c.)+U\sum_i(n_{i\uparrow}-\frac{1}{2})(n_{i\downarrow}-\frac{1}{2})$ where the sum is ...
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0answers
49 views

Many-particle operators in the occupation number representation

I've read that if we have a many-particle operator in the coordinate representation which is the sum of identical one-particle operators operating, however, on different particles, like $\hat{Q} = ...
2
votes
1answer
234 views

What favors island growth of a sputtered material?

What would be the best choice of parameters in general if one would like to get pure island growth (i.e. Volmer-Weber growth) in a sputtering deposition process and what would be a good estimate of ...
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0answers
48 views

Intuitive meaning of Matsubara frequencies

I have a somewhat nebulous question but I hope you'll bear with me. I am trying to understand about how to think about Matsubara frequencies and the imaginary time formalism in an intuitive way. That ...
2
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2answers
157 views

Phonon spectrum

I had a question regarding phonon spectrum in condensed matter. Consider a cubic lattice with '$p$' atoms per primitive cell. Consider the lattice plane used for derivation of the phonon spectrum to ...
8
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4answers
95 views

Can a material made of a heavier isotope of an element become harder or stronger?

I was wondering if any experiments have been done to measure if there is a change in the hardness or strength of a material made solely of a heavier isotope of an element which is a constituent of the ...
3
votes
1answer
33 views

What does a bucked honeycomb lattice mean?

I was going through some literature where they have mention about bucked honeycomb lattice, but I was unable to understand about the bucked honeycomb term.
3
votes
1answer
260 views

effective field theory of the projective semion model

The "projective semion" model was considered in http://arxiv.org/abs/1403.6491 (page 2). It is a symmetry enriched topological (SET) phase. There is one non-trivial anyon, a semion $s$ which induces a ...
2
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1answer
41 views

Green Kubo formalism valid for inhomogeneous systems?

I'm interested in nano-composites and their effective properties and I use classical Molecular Dynamics as computation method. My question is: "Can I still use the Green Kubo formula to calculate ...
3
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0answers
30 views

Is $PT$ always a symmetry in (2+1)D?

Is the combination of parity $P: (x,y,t)\to (-x,y,t)$ (sometimes also called reflection $R$) and time reversal $T: (x,y,t)\to (x,y,-t)$ always a symmetry in (2+1)D theories with Lorentz or Galilean ...
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0answers
34 views

If BdG Hamiltonian has particle-hole redundancy, how can it be trusted in discussing the topological properties of superconductors?

In BdG Hamiltonians, the particle-hole symmetry is not a true symmetry but rather a redundancy of description. In my oppinion, saying with the presence of particle-hole symmetry is just saying: hey, ...
3
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0answers
41 views

Can the occupation of Floquet bands be calculated from the Keldysh Green's function?

A periodically driven band structure can be semiclassically described by Floquet theory, resulting in photon-dressed Floquet bands (non-equilibrium steady states). Usually, for non-equilibrium ...
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vote
1answer
35 views

Elastic properties of materials at low temperature

It is common knowledge that materials are more brittle at low temperature. But does it apply also on elastic deformations or is it just matter of plastic deformations? Practically: Is it possible to ...
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0answers
43 views

Kondo effect and poor man scaling

I am working on Kondo problem, using poor man scaling. The feynman diagram representation is given below. First process is direct scattering of conduction electron while 2nd is creation of ...
3
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0answers
29 views

Can different Floquet replicas be distinguished (within Floquet's theorem)?

According to Floquet's theorem, two quasi-energies separated by $n\hbar \omega$ represent the same state. According to this, I would think different replicas are indistinguishable experimentally. ...
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0answers
27 views

References on Josephson ring modulators

I would like some good references on Josephson junctions and, in particular, Josephson ring modulators. I know that Devoret has written a handful of papers and notes on JJs, but I am hoping to find ...
3
votes
2answers
102 views

Difference between DMRG (density matrix renomalization group) and MPS (matrix product states)?

I am learning DMRG recently. I noticed there are many papers both in the DMRG approach and MPS (such as variational matrix product state (VMPS) by F.Verstraete and J.I.Cirac) approach. In my eyes, ...
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0answers
18 views

Diamagnetic materials are very rare, compared to paramagnetic and ferromagnetic materials, right? [closed]

For a material to be diamagnetic, it should have zero intrinsic magnetic dipole. Therefore, most materials are not diamagnetic, right?
2
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1answer
243 views

Why does graphene exist?

I started to read some articles on graphene and almost all say that graphene was discovered late because physicists thought it would be unstable. Despite this, I didn't found a clear explanation of ...
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0answers
59 views

What will a glass look like in 500 years?

The glass is in a metastable state. It is changing constantly. So what will a piece of glass look like in 500 years in room temperature?
3
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3answers
65 views

Relation between boiling, vapour pressure and atmospheric pressure

The boiling point of water is always defined as the temperature at which the vapour pressure of water is equal to the atmospheric pressure. How does the definition relate to why there is intense ...