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

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Why no thermal expansion for camping tents?

I know that solid materials expand when heated, which is called thermal expansion. But what is happening to tent square or tent canvas of (plastic?) camping tents? I have noticed, that during the ...
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13 views

Effective Potential of experienced by a particle with contact interaction in an optical lattice

Suppose i have an optical lattice with particles loaded onto it, the potential due to the optical lattice is $V_{0}Cos\left(x\right)$. Assume that the particles interact with eachother through contact ...
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27 views

Bosons are either gapped or condensated, except physical principle protected cases (Goldstone boson, photon)?

Bosons are either gapped or condensated, except physical principle protected cases (Goldstone boson, photon, etc.)? I read this in a paper (version1 of http://arxiv.org/abs/1404.3728v1, 1st page 1st ...
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36 views

Why does inelastic X-ray scattering probe the longitudinal dielectric function as opposed to the transverse dielectric function?

Light is a transverse wave. Therefore, light in the optical range (i.e. visible light) couples to transverse collective excitations of a material when measuring the optical conductivity for instance. ...
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22 views

Has anyone experimentally shown the quantized thermal hall conductivity in Quantum Hall systems?

For background: In a $D=2+1$ state with edge modes described by a chiral $( c_L \neq c_R )$ CFT there is a predicted thermal Hall conductance associated with the gravitational anomaly at the edge. ...
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33 views

Quasicrystals - Projections from higher dimensional regular crystal lattices

Why are quasicrystals projections from higher dimensional regular crystal lattices? See for example wikipedia: »Mathematically, quasicrystals have been shown to be derivable from a general ...
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20 views

why does muon hop rate in metals change with temperature like this

you can find this figure in this pdf we use μSR to study the superconductor properties,,but I don't quite understand the T^-9 slope, does muon trapped in an interstitial site and hop rate drop with ...
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1answer
59 views

How does pressure influence temperature in liquids?

Lets say we have a tank with a fixed mass of liquid at atmospheric pressure and room temperature. How do we influence the temperature when we exert pressure (e. g., with a piston) on the liquid? Are ...
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4answers
83 views

Ohm's Law: Drude Model

For a very long time now, I've been thinking about the Drude Model derivation of Ohm's Law. I know that a rigorous derivation requires a Quantum Mechanical approach. However, the mere fact that the ...
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2answers
41 views

Correlation in electron gas

In the textbooks that I read (namely Ashcroft/Mermin , Marder, etc.) it seems that a distinction is made between the correlations in electron gas and a Couloumb interaction between the electrons. What ...
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2answers
40 views

Thomas - Fermi screening

I read in Ashcroft & Mermin's Solid State text that for the Thomas-Fermi approximation to be applicable, the external potential needs to be "slowly varying," What does it mean for a function (in ...
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33 views

Spin wave theory for 1D spin systems

In general, when one performs spin-wave theory, he has to assume some kind of long-range ordered state and perform spin-wave theory (using for instance Holstein-Primakoff bosons) around that state. ...
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49 views

Chirality of Weyl Semimetal

For Weyl semimetal, the effective Hamiltonian reads: $$H=E_0 \mathbb{1} + v_0 \cdot \mathrm{q} \mathbb{1}+\sum_{i=1}^{3} \mathrm{v}_i \cdot \mathrm{q} \sigma_i$$ Why is the chirality given by ...
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35 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. I have the following question: Is the ...
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1answer
27 views

Mapping a continuum XY model to a discrete one

A low energy expansion of a system I am currently investigating is described by this XY-like model: $$ H_1 = \int_0^\beta \mathrm{d} \tau \int_{\left[ 0, L \right]^2} \mathrm{d}^2 x \left( J \left( ...
4
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1answer
279 views

Do all the electrons form Cooper pairs at absolute zero?

At $T=0K$, do all the electrons form Cooper pairs, or just the electrons near the Fermi Surface do?
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40 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 ...
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17 views

Excitations of a quantum spin-liquid

I have a simple (yet perhaps profound ?) question related to the physics of quantum spin liquids (QSL). These states of matter are "defined" as state that do not break any symmetry of the Hamiltonian ...
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1answer
50 views

Ground state Phase Diagram of Bose-Hubbard Model

The Hamiltonian of Bose-Hubbard model reads as $$H=-J\sum\limits_{<i,j>}b_i^{\dagger}b_j+h.c.+\frac{U}{2}\sum\limits_{i}n_i(n_i-1)-\mu\sum\limits_in_i~~~~~~~~~(1)$$ For this we plot phase ...
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1answer
33 views

Why does proximity to a superconductor open a gap in the surface states of topological insulators

I have read in many places that the gapless surface states of 3D topological insulators are robust to perturbations which do not break time-reversal symmetry. I have recently also seen many papers ...
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27 views

Is that possible to derive Landau-Fermi liquid theory from microscopic equation?

The question arised from reading Wen's book "Quantum Field Theory of Many-body Systems (Oxford 2004)" p204 To appreciate the brilliance of Landau-Fermi liquid theory, let us look at the ...
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1answer
45 views

SPTs and systems with Topological Order

I am an undergrad interested in Condensed Matter Theory. Particularly topological phases and systems exhibiting topological order. A potential research advisor doing a lot of work in Symmetry ...
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4answers
427 views

How does the speed of electrons change around a circuit?

I have been thinking about ways of teaching electronics and I'm wondering if the following is true... For starters, when we talk about voltage as energy per unit charge, is this energy manifest ...
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26 views

Ising formulation of the graph isomorphism problem

Context I have been going through Ising formulations of many NP problems by Andrew Lucas. In section 9 on page 22, the author gave an Ising formulation of the graph isomorphism problem. Here I ...
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46 views

Question about bosonization method

I have a question about bosonization method used in 1D system. Generally the bosonized field is assume to the following form \begin{equation} \psi = e^{i\phi}, \quad \phi = \phi^\dagger ...
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1answer
32 views

Atomic physics - lattice energy

Question: Why is ionic lattice energy inversely proportional to the radius of the atom? Most heterogeneous covalent molecules are polar to some extent. The degree of polarity, or the dipole moment, ...
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1answer
27 views

Neutron Diffraction Device

I was just wondering if we have a beam of neutrons, lets say of various energies meeting or colliding with a powder of monoatomic crystallites, what would happen to the neutron beam and the energies ...
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1answer
74 views

can gapped systems have gravitational anomalies?

The question is in the title. If it is possible, what are some examples of gapped systems--either quantum field theories or condensed matter systems--which exhibit some kind of anomaly when coupled ...
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48 views

Why is the Hubbard model written down so late?

It is just the tight binding model plus on-site interaction. What prevented people from arriving at the Hubbard model?
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1answer
45 views

Evaluating low-temperature dependence of the BCS gap function

How does one go about evaluating the behavior of the BCS gap $ \Delta = \Delta(T) $ for $ T \to 0^+ $ under the weak coupling approximation $ \Delta/\hbar\omega_D \ll 1 $? In Fetter & Walecka, ...
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1answer
38 views

Capillary action meniscus height in a tube fitted inside another tube?

I was thinking about how would capillary action change in a tube (classic example) and in a tube fitted inside another tube (considering water as the liquid involved). Height of liquid column: ...
4
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31 views

How to distinguish Bose glass and superfluid phases in a harmonic trap?

In mean-field study of Bose-Hubbard model in an optical lattice, what parameter can be calculated to distinguish Bose glass and superfluid in a harmonic trap?
4
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1answer
57 views

Do metals have their distinctive look because of the electron sea which surrounds the metal atoms?

are metals shiny because of the electron sea which surrounds the atomic lattice of the metal sample. are metals more shiny because the electron are more evenly distributed on the surface?
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Is an object's color/shine/texture dependent on its electrons only? If electrons are same then why are there so many different colors?

when we look at an object be it a metal or a non-metal are we looking at its electrons only, so then if all electrons are same then why do different chemicals or elements or objects have different ...
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2answers
75 views

Is the magnetization direction of a permanent magnet fixed?

I am now playing with a permanent magnet made of Neodymium. It is impressively strong. A question is, is the magnetization direction of the magnet fixed relative to its crystal structure?
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23 views

Physical, intuitive reason for divergence of dielectric constant at electronic percolation transition?

Several papers such as this (warning, PDF) and this (PDF again) talk about how, near the electronic percolation transition for a metallic 2D film, the real part of the dielectric constant diverges ...
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20 views

What is the general conditions for non-zero polarization?

I only know that for a system to have non-zero polarization it should break inversion symmetry. What about others requirements?
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1answer
42 views

Does the Night Mode of the screen display (LCD) save more energy?

In some cases, we can enable the Night Mode (reversing the bright and dark color of the display; such as White Text, Black Background) for the screen display. LCD(Liquid-crystal display) seems to be ...
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1answer
108 views

What do we mean when we say Bose condensation? And why can't fermions condense if they don't pair?

In common textbooks, we are told that bosons can condense in a single-particle state because of bose statistics and when the system undergoes a bose condensation, the bose field operator obtains a ...
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1answer
72 views

Difference between the 'phonons and virtual photons'

I understand what are virtual photons and the difference between the real and virtual photons. However, I am not able to clearly distinguish the difference between the 'phonons and virtual photons'. ...
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1answer
89 views

What are the current contenders/most promising approaches to High Tc Superconductivity?

I want to know what kinds of things theorists are currently looking at. Specifically, I want to know more about the promise that field-theoretic methods are showing. I am studying superconductivity at ...
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11 views

Why do ferromagnetic thermocouples change their behaviour near the Curie point?

Having read Wikipedia's current explanation that certain types of thermocouple (specifically Type K thermocouples) experience a step-change in their potential when they reach the Curie point of the ...
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40 views

Graphene Chern number for Dirac nodes

Why do we add winding number at two Dirac nodes to determine topological phase?
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1answer
64 views

Matsubara Frequencie

I have to evaluate the following Matsubara sum: $$\frac1\beta \sum \left(\omega^2 +a^2\right)^{-1}$$ for Bosonic-Matsubara frequencies. I know contour integration it the way to go. Therefore, I ...
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1answer
45 views

Interchaging boson and fermion on an infinite 1 dimensional line

In 1+1 dim bosonization, one introduce the Klein factors, which are Hermitian and satisfies Clifford algebra. (1) In the case of 1 dim space is a 1D ring ($S^1$ circle), then one have left-right ...
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48 views

Mean-field theory : variational approach versus self-consistency

I have a general question concerning mean-field approaches for condensed matter classical of quantum statistical mechanic systems. Does determining the mean-field by a variational approach always ...
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0answers
23 views

How to isolate and verify the source of optical absorption/effects?

This is similar to my other question, but not the same -- that one was about the energy ranges of various absorption mechanisms, and this one is more about experimental techniques to find them. Let's ...
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6 views

Condensate fraction and momentum distribution in cold atom experiments

In ultrcold atom experiments, people usually use time-of-flight technique to measure the momentum distribution, then get the condensate fraction information from the interference pattern. What is the ...
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1answer
41 views

What does it mean for electrons to be “diffusive”?

I'm reading this paper and it has the line (end of 3rd paragraph, page 2): It turns out that the simple fact that electrons are diffusive instead of freely propagating leads to a profound ...
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Proximity effect and integrating out the quasiparticle degrees of freedom

I am reading at the moment the paper http://arxiv.org/abs/1401.5203 and try to reproduce the results. One result is the proximity correction $S_{\Sigma}$ to the system $$ e^{-S_{\Sigma}} ...