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

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What is the difference between crystals and solid? [on hold]

In condensed matter physics, what are the differences between crystals.
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Why Weyl fermion in Weyl semimetals(WSM) have high mobility only at low temperature?

I read several papers reporting high Weyl fermion with very high mobility in WSMs such as TaAs, NbAs, WTe2 and so on. However, this high mobility looks like (=Weyl fermion) always appears at only low ...
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50 views

Relationship between crystal momentum and true momentum

Most textbooks make it clearly that crystal momentum is not true momentum. However, in a lot of literature, crystal momentum is treated as true momentum. Here's two examples: Rashba spin splitting. ...
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2answers
64 views

How can one intuitively understand formulas of the form $χ\sim\sum_{\bf k}{f_{\bf k}-f_{\bf k+q}\over ε_{\bf k+q}-ε_{\bf k}}$?

When calculating various susceptibilities, we get below formula again and again. $$\chi( {\bf q},0) \sim \sum\limits_{\bf{k}} {\frac{{{f_{\bf{k}}} - {f_{{\bf{k}} + {\bf{q}}}}}}{{{\varepsilon _{{\bf{k}}...
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29 views

Decomposition of the Time-Evolution Operator: Translationally Invariant MPO

Hello everyone myself Sudipto. Currently I'm learning the matrix product state technique in order to simulate 1d spin system and study different properties of the system form quantum information ...
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2answers
41 views

Why alloy have more resistance?

Is there any simple way to understand why alloy have more resistance than metals? My teacher ask this, I answer that, there might be more free electrons in metals than an alloy, but she said you are ...
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1answer
43 views

Vacuum persistance amplitude

E. Fradkin's Field Theories in Condensed Matter Physics formulas 3.57 and 3.58: I feel really sad about it, but all my tries of getting from formula $$ Z = \operatorname{tr} \hat{T} \prod_{j=1}^{...
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37 views

Is there a block spin renormalization group scheme that preserves Kramers-Wannier duality?

Block spin renormalization group (RG) (or real space RG) is an approach to studying statistical mechanics models of spins on the lattice. In particular, I am interested in the 2D square lattice model ...
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38 views

Interpreting conical intersection in quantum adiabatic evolution [on hold]

Recently, I have studied a particular quantum adiabatic algorithm. When I plot the eigenvalues of the ground and first excited state against normalized time $s$, there appears a conical intersection. ...
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2answers
58 views

How do signals go through solid objects? [closed]

So many types of signals pass, or seem to pass I don't know, through solid objects. How do they do this?
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36 views

RPA Charge Instability in One Dimensional Electronic Systems

As we know, no long range order in a one dimensional electron system is expected due to quantum fluctuation. A typical 'phase diagram' for a system with short-range interactions is shown on page 69 of ...
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9 views

Orthogonality condition between core and valence states (pseudopotentials)

In the paper "Pseudopotential methods in condensed matter applications" by W. E. Pickett the author comments the following in the introduction section (Page 4, 1st paragraph - introduction) "Although ...
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21 views

Deriving Reciprocal Lattice Definition

The derivation of reciprocal lattice vectors in terms of the direct space lattice vectors starts by applying expanding a translationally invariant lattice function $f(\bf{R_k}+r)$ in plane waves $f_k ...
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33 views

Bosonization for unequal left/right Fermi velocities

The standard exposition of bosonization/Luttinger liquid theory in textbooks treats the case that left and right channels share the same absolute value of Fermi velocity. Is it possible to relax this ...
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0answers
13 views

Will two Weyl points which belong to a Weyl pair be transformed to each other by inversion symmetry?

In solid state system, A Weyl pair can be obtained by splitting a Dirac node when time reversal symmetry is broken and inversion symmetry is reserved. My question is that Whether the inversion ...
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0answers
229 views

Intuition behind transforming a Hamiltonian expressed in momentum representation in eigenbasis [closed]

This question is a supplement to a previous question on the same paper. In the section 4.1 of Quantum Computation by Adiabatic Evolution, Farhi et al proposes a quantum adiabatic algorithm to solve ...
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1answer
34 views

Is edge states of topological insulators superconducting?

I am told edge states of topological insulators are free from back scattering. Does this mean topological insulators have no resistance if only edge states are taken into account?
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1answer
42 views

Connection between fractional charge and Schrodinger's cat

In the FQHE, it is said that one electron splits into three 1/3-charged entities. Is it like the Schrodinger cat?
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41 views

Density of States for a separable hamiltonian

There are $N$ non interacting electrons in a potential well: \begin{align} H&= -{1 \over 2 } \nabla^2 + U(x,y,z) \\ U(x,y,z)&={1\over2}\omega^2z^2 \; \mbox{for} \; (x,y) \in [0,L]\times [0,L]; ...
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At most $N$ gapless charge/spin modes in a system of $N$ coupled 1D chains?

Leon Balents and Matthew P. A. Fisher claimed the following without any further explanation ($N$ is the number of chains) For a system of $N$ coupled 1D chains, the number of gapless charge modes ...
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8 views

What kind of flux-pinning effect will occur if a type two superconductor is subjected to an AC electromagnet?

When a supercooled type two superconductor is subjected to a static magnetic field, the superconductor pins to the flux of the field (the mixed-state meissner effect is apparent). What happens if it ...
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1answer
69 views

Specific heat of the classical ferromagnetic Heisenberg model

I have simulated the classical ferromagnetic Heisenberg model on a cubic lattice using Monte Carlo and I get a finite specific heat near zero temperature. My understanding is that from the magnon ...
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41 views

Hubbard Model. Spin Operators.

In a book Field Theories of Condensed Matter Physics author (p.10 of second edition) defines spin operators as: $$ \vec{S}(\vec{r}) = \frac{\hbar}{2}c_{\sigma}^\dagger(\vec{r})\vec{\tau}_{\sigma\...
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1answer
120 views

Replacing fermionic operators with their Fourier transform and boundary conditions

In the section 4.1 of Quantum Computation by Adiabatic Evolution, Farhi et al proposes a quantum adiabatic algorithm to solve the $2$-SAT problem on a ring. To compute the complexity of the algorithm ...
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0answers
85 views

Some questions about the Kitaev Chain Model

In the paper,'Unpaired Majorana Fermions in Quantum Wires', Kitaev shows that unpaired Majorana Modes can be found at the end of a Quantum Wire for certain conditions. The effective Hamiltonian ...
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34 views

Tight binding Hamiltonian in the k-space

I want to find the band structure of this 2 dimensional lattice which isn't completely flat: Using a tight binding model.And take unit cells as they are shown in the figure. And assuming that each ...
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40 views

Why does Fermi Level change due to change in donor atom concentration?

Suppose I have a n-type semiconductor whose fermi-level lies (say) 0.2 eV below the conduction band. Why would this level change if I changed the doping by making the donor concentration (say) 4 times ...
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How does from the curvature of the energy surface, different phases of matter can be identified?

I have recently started reading about the topological order in condensed matter. I am trying to understand the role of topology of the energy surface in distinguishing the different phases of matter. ...
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1answer
19 views

Is a typical glass slide really amorphous or does it just have very small crystallites?

I heard today that there's not really any true amorphous materials; that the theoretical concept (no level of ordering whatsoever) exists of course, but that no materials are 100% truly random and ...
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1answer
97 views

Calculating the boundary modes in Kitaev Chain

In section 2 of the paper, 'Unpaired Majorana Fermions in Quantum Wires', equation (14), the following transformation: \begin{equation} b^{'} = \sum_{j} (\alpha_+ ^{'} x_+ ^{j} + \alpha_- ^{'} x_- ^{...
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62 views

Confused about the substitution of the fermionic operators with their Fourier transform in an adiabatic Hamiltonian

In the section 4.1 of Quantum Computation by Adiabatic Evolution, Farhi et al proposes a quantum adiabatic algorithm to solve the $2$-SAT problem on a ring. To compute the complexity of the algorithm ...
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53 views

Why is there a state which is annihilated by two different operators with same absolute Fourier index?

In the section 4.1 of Quantum Computation by Adiabatic Evolution, Farhi et al proposed a quantum adiabatic algorithm to solve the $2$-SAT problem on a ring. To compute the complexity of the algorithm ...
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1answer
33 views

Reasoning behind taking the Fourier transform of the fermionic operators for a circular $1$D spin chain [closed]

In the section 4.1 of Quantum Computation by Adiabatic Evolution, Farhi et al proposes a quantum adiabatic algorithm to solve the $2$-SAT problem on a ring. To compute the complexity of the algorithm ...
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1answer
28 views

Boundary value condition used during Jordan-Wigner transformation for a $1 D$ Ising chain

In the section 4.1 of Quantum Computation by Adiabatic Evolution, Farhi et al proposes a quantum adiabatic algorithm to solve the $2$-SAT problem on a ring. To compute the complexity of the algorithm ...
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1answer
48 views

Reason behind choosing the invariant states for an operator which commutes with an adiabatic Hamiltonian

In the section 4.1 of Quantum Computation by Adiabatic Evolution, Farhi et al proposes a quantum adiabatic algorithm to solve the $2$-SAT problem on a ring. To compute the complexity of the algorithm ...
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2answers
97 views

Partition function and coherent state path integral

I have been working through the derivation of the partition function expressed as a path integral in terms of coherent states, following the many-body condensed-matter field theory books of Altland &...
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30 views

Why do the singularities of the thermodynamic functions expected to be non-negative powers?

I am going through the first chapter of Exactly Solved Models in Statistical Mechanics. On page 4, at the end of section 1.1 it is said that: I would like to know the basis of this expectation. ...
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1answer
64 views

Is zero heat capacity possible without violating the third law of thermodynamics?

Suppose we have a gapped system i.e. no gapless excitation is possible. If the thermal energy is insufficient to excite atoms from ground state to excited state of any kind (of a single atom or of a ...
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1answer
65 views

Kitaev Chain Spectrum (Unpaired Majorana Fermions in quantum wires) [closed]

How does one arrive at the spectrum equation(13): $$\epsilon (q)=\pm \sqrt{(2w \cos q +\mu)^2+4\cdot \mid {\Delta} \mid^2 \sin ^{2} q}$$ from the initial Hamiltonian. Also, shouldn't (12) in the ...
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Derivation of zero temperature conductivity in Dirac materials - Einstein formula

I've come across this in multiple papers but have no idea where this comes from. For the Dirac materials the zero temperature conductivity $\sigma$ can then be expressed as $\sigma = e^2v_{F}^2D\ \...
2
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1answer
74 views

Why does $\prod^n_{j=1}\sigma^{(j)}_x$ commute with this adiabatic Hamiltonian? [closed]

In the section 4.1 of Quantum Computation by Adiabatic Evolution, Farhi et al proposes a quantum adiabatic algorithm to solve the $2$-SAT problem on a ring. The adiabatic Hamiltonian is defined as $$...
4
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1answer
86 views

Ground state of an adiabatic Hamiltonian as an eigenstate of the total spin

I am going through Quantum Adiabatic Evolution Algorithms with Different Paths by Farhi et al. Here, the authors propose to add a special term to the adiabatic Hamiltonian so that the path of the ...
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1answer
20 views

Experimental confirmation of the finite jump of the occupation number at the Fermi surface

It is a well-known result in Fermi-liquid theory that the occupation number has a finite jump at the Fermi surface. But, is it confirmed experimentally?
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1answer
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Finding explicit unimodular transformations for Chern-Simons K-matrices

An invertible, symmetric matrix with integer entries, $K$, that encodes the braiding and statistics of an Abelian topologically ordered state, is equivalent to another such matrix, $K'$, if there ...
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1answer
35 views

Question about the Luttinger liquid

I am learning Luttinger liquid now. It is a very basic question, I think. Look at the figure. For each $k $, there is a state for the left mover and a state for the right mover, right? They have the ...
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48 views

Improved gap estimates for quantum adiabatic evolution

In his PhD thesis, Daniel Nagaj mentioned that Deift† et al has tightened the relationship between the adiabatic evolution time $T$ and the energy gap between the ground state and first excited state, ...
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High pressure deformation of metals

Does copper undergo elastic recovery after being exposed to high pressures (above 30 GPa in a diamond anvil) at room temperature?
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1answer
43 views

What is the Single Mode Approximation?

When Girvin and co-workers solved the excited collective modes called magneto-rotons in Fractional Quantum Hall liquids, they used something called the Single Mode Approximation (SMA). My question is: ...
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1answer
96 views

Why is Wick contraction a $c$-number?

It is mentioned in Fetter's Quantum Theory of Many-Particle Systems (in contraction part of section 8 Wick's Theorem), that: contractions are c numbers in the occupation-number Hilbert space, not ...
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1answer
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Computing the density operator commutation relations (Atland & Simons)

I'm trying to work through Altland and Simons' example of interacting fermions in one dimension. It's in chapter 2, page 70 (you can find it here). They define fermionic operators $$ a_{sk}^\dagger $$...