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

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What are fragmented condensates?

It is defined that if more than one eigenvalue of the one-body density matrix are macroscopically occupied the condensate is said to be fragmented. $$ n^{(1)},n^{(2)},...=\mathcal{O}(\mathcal{N}) $$ ...
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63 views

Fetter & Walecka's derivation of second quantised canonical Schrodinger equation for fermions

On page 18, before the occupation number variables for states i and j are changed $n_i \rightarrow n'_i = n_i - 1$ and $n_j \rightarrow n'_j = n_j + 1$ respectively, could we not have rewritten eq. ...
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22 views

How well can ADSCFT related approaches to condense matter predict measurable properties of materials? [closed]

Are ADSCFT techniques able to make any predictions about measurable properties of any materials? Are there some interesting but somewhat accessible looking problems left in this area to solve or is ...
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0answers
22 views

Non-equilibrium electronic distribution in the time-relaxation approximation - Which is the boundary condition?

In Chapter 13 of Ashcroft-Mermin - "Solid State Physics", the following non equilibrium electronic phase-space distribution for the semiclassical electrons in a periodic crystal is derived: ...
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73 views

Transfer from Heisenberg to Ising model

It is well know, that ferromagnets can be described using Hamiltonian $$ H = -\sum\limits_{i<j}J_{ij}\, (\mathbf{s}_i \cdot \mathbf{s}_j). $$ where (three dimensional) spins $\mathbf{s}_i$ ...
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1answer
32 views

What's the difference in the film between sputtering deposition and an ebeam evaporator?

I know the differences between the two deposition techniques, but what about the difference in the properties of the resulting films? All things being equal (such as substrate temperature), would ...
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1answer
87 views

Difference between $\nu=5/2$ quantum Hall state, chiral p-wave superconductor, He 3

I am interested in the relation between the following three phases of matter (in 2D): chiral $p$-wave superconductor (spineless $p_x + i p_y$ pairing) $\nu=5/2$ fractional quantum Hall state A-phase ...
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16 views

What is our most complete microscopic theory for the elastic-plastic transition point?

I suppose its all stated in the title. What is our most successful description of the microscopic behavior of material at the elastic-plastic transition point. My condensed matter physics prof was ...
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38 views

Quantum spin Hall effect and the edge states

In quantum spin Hall effect or Kane-Mele model, how can one get rid off the edge states without affecting the bulk?
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1answer
38 views

behavior of dissolved ionic compounds in an electric field

Consider the following setup - An open, insulating box is filled with distilled water, into which is dissolved a significant amount of pure NaCl. Two insulated lumps of conductor, one with a large ...
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47 views

Electron self-energy calculation for a $k$-dependent interaction

I am trying to calculate the Fock term of an electronic self energy in the Matsubara formalism : Where the straight black line in the free electronic Green's function : $G_{k+q}(i\omega_n + i\nu_n) ...
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27 views

Do tensor product tables for irreducible representations apply for non-symmorphic space groups?

I'm reading Dresselhaus's book on group theory for solid-state physics, but I'm having trouble understanding how to get irreducible representations for phonons away from $\mathbf{k} = \mathbf{0}$ for ...
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30 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. ...
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57 views

How to describe spin-orbital coupling in Weyl semi-metal

In three dimensional Weyl semi-metal, the Hamiltonian that describes low excitation quasi-particle is well-know Weyl Hamiltonian: +/- $k\cdot\sigma$. But if I want to add spin-orbital coupling in that ...
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1answer
131 views

Kronecker sum or direct sum?

When we write $$H=\sum_k H_k$$ in condensed matter physics, are we using Kronecker sum or direct sum? I think this is direct sum. However, Wikipedia says it is Kronecker sum. Can anyone give some ...
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26 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?
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1answer
112 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 ...
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1answer
24 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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43 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 ...
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89 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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13 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?
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1answer
187 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 $N\times N$ matrix- Here $E$ is the onsite energy and $t$ is the hopping ...
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21 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 ...
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1answer
48 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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26 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, ...
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63 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 ...
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59 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 ...
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53 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} = ...
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59 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 ...
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1answer
42 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.
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4answers
107 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
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0answers
73 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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74 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, ...
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58 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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1answer
49 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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57 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 ...
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1answer
63 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 ...
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36 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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29 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 ...
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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?
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3answers
113 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 ...
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65 views

Reverse-engineering an equation of state

Suppose we have a fluid of some kind with a (let's keep it simple) barotropic equation of state: $p = p(\rho)$. Typically, I see that one starts with a function $p$ and $\textit{then}$ solves the ...
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1answer
83 views

“distinguishability” of 1D identical particles

Recently when I deal with 1D electron system, it occurred to my mind that since these electrons are not able to bypass each other during the scattering processes, we can actually label them as the ...
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49 views

2-loop $\phi^4$ at finite temperature [closed]

When evaluating diagrams that contribute to the 2-loop effective potential $V_{eff}$ in $\lambda \phi^4 $ theory at finite temperature one has to calculate diagrams of such type which equals to ...
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2answers
57 views

Translating Electronic Bands back to first Brilluoin Zone

For phonons, I understand why we can translate everything back into the first Brillouin Zone: there is a minimum wavelength defined by two lattice sites. For electrons, which are delocalized, I see ...
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14 views

Diffusive or balistic? Spread of the wave packet when localized and extended states coexist

If the lattice is perfectly periodic, then the wave packet of a particle initially located on a site spreads balistically. Namely, its size increases linearly in time. Now, introduce disorder into ...
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44 views

Reference for open XX spin chain with external magnetic field

I would like a reference on the diagonalization of an open XX spin 1/2 chain with homogenous external magnetic field. I am new to the subject and I haven't been able to find a reference for it. Edit: ...
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1answer
83 views

Soft Condensed Matter book for self study

I'm a junior undergraduate in physics & materials science. I've had half of a course in quantum mechanics taught out of Townsend's book (We've gone from beginnings of matrix mechanics to the ...
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60 views

Numerical problem with Hartree-Fock equations for dilute Bose gas

I have to solve the following set of equations self-consistently: $$\begin{align} n_c(\mathbf{r}) & = \frac{1}{g}\left[\mu - V_{\rm ext}(\mathbf{r}) - 2 g n_{T}(\mathbf{r}) \right] \\[3mm] ...
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112 views

Is there a database or a classification of High-temperature superconductors?

I was wondering if there exists a list with all (or most of) the High-$T_c$ superconductor materials. In particular I'd like to know if there are databases or review that classifies them by their ...