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

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21
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3answers
4k 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 ...
2
votes
1answer
653 views

How do you obtain the commutation relations at non-equal times (for the edge of a fractional quantum Hall state)?

The edge of a fractional quantum Hall state is an example of a chiral Luttinger liquid. Take, for the sake of simplicity, the edge of the Laughlin state. The Hamiltonian is: $$H = ...
1
vote
1answer
313 views

“Classical” limit of Quantum Hall Effect

Imagine a partially filled $\nu=1$ state of the integer quantum Hall effect (IQHE). One way to think about it is to imagine a gas of electrons where each particle is locked to the lowest quantum state ...
5
votes
1answer
207 views

What is the energy functional for $\nu=5/2$ Moore-Read state?

I am trying to do some Monte Carlo simulations for Pfaffian state from Fractional Quantum Hall effect. I am wondering what is the energy functional for $\nu=5/2$ Moore-Read state?
1
vote
1answer
171 views

Heuristic argument for the temeprature dependence of specific heat in the “low” temperature regimes

Here by "low temperature" I meant it in the scale of the characteristic $\hbar \omega$ of the system. One can calculate and show that in the low temperature regime $C_V$ of phonons goes like $T^3$ ...
2
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1answer
220 views

Fourier analysis in crystallography

What is the best reference for an introduction to the use of Fourier analysis in crystallography?
2
votes
2answers
324 views

Identifying a critical phenomena?

I have a system with a number of measurables (in time). Some measurables are discrete some are continuous (within the measurement accuracy). How can I determine whether my system experiences ...
6
votes
1answer
368 views

Glass and isotropy

Glasses are amorphous materials. Nevertheless, as far as I know, in some areas of Condensed Matter, they consider that the glass is isotropic. Under what restrictions they can do this assumption? ...
7
votes
2answers
1k views

Free particle in magnetic field / Landau quantization

I have a question concerning a possible derivation of the Landau quantization. In our lecture notes (and some other places as well), the following ansatz is used: $$ \Psi(x,y,z) = ...
8
votes
1answer
241 views

BCS wave function in Neutron stars

I've heard mentioned in various classes that neutron stars, like superconductors, are described by BCS theory. I know that in superconductors a key element in forming cooper pairs is a net attractive ...
5
votes
1answer
716 views

How does spring constant change with resistivity changes

I want to create a set of silicon based materials that have been doped with different materials and/or different amounts of dopants. The purpose of this is to see how the spring constant of silicon ...
1
vote
0answers
378 views

1D Topological insulator with PT symmetry

Assume I have the Hamiltonian for a 1D topological insulators as: $H=sin(P_x) \sigma_x+i \Delta \sigma_{y}+(1-m-cos(P_x)) \sigma_z $ where $m$ is the mass term, $P_x$ is the momentum and $\Delta$ is ...
8
votes
1answer
612 views

A better conceptual model for cooper pairs in a superconductor

The conceptual model I have been introduced to for cooper pairs in a bulk superconductor is what I would call the "wake" model, where one electron deforms the positively charged lattice, changing the ...
2
votes
1answer
125 views

Effect of a external EM field on a dielectric

If an external EM field (a laser, for example) act on a dielectric (a glass, for example) what will be the effect of this field on the dielectric constant and on the refractive index of the material? ...
7
votes
0answers
319 views

Descent equation and anomaly polynomial

I am just reading Ryu, Moore and Ludwig's paper on classifications of topological insulators and quantum anomaly. They are trying to relate the quantum anomaly as a signal of the presence of a ...
6
votes
1answer
445 views

Expansion of multi-particle state vector as a sum of n-entangled states

Physically, quantum entanglement is ranged from full long-range entanglement (Bose-Einstein condensate), described by a basis of states that look like this: $$ |\Psi\rangle = |\phi_{i_{0} i_{1} ... ...
4
votes
1answer
583 views

$\theta$ term of anomaly related with topological insulators

I am reading Ludwig's paper "Electromagnetic and gravitational responses and anomalies in topological insulators and superconductors", and in this paper, although I am clear how they get the descent ...
6
votes
1answer
925 views

When is use of the 'effective mass' concept appropriate?

In textbooks the characteristic length scale of an exciton, or an electron bound to dopant atom, in silicon is calculated by analogy to the vacuum case. Bohr radius in vacuum: $$a_0 = \frac{4 \pi ...
5
votes
3answers
238 views

Mobile “muonic hydrogen”

If we look at the atomic positions in a single crystal sample with a diamond like lattice, there exist directions along which there are long hexagonal "tubes" (I'm not sure if these have a proper ...
7
votes
2answers
547 views

How far away are we from resolving high temperature superconductivity?

What are the major recent findings and their corresponding contributions to an overall picture? How well explained are the various regions of the dome, is there any thing that is pretty well ...
5
votes
1answer
209 views

Is it true that the angular momentum of electromagnetic waves in an anisotropic medium is an integral of motion?

Extending my previous question Angular moment and EM wave, does it make sense to talk about the angular momentum of electromagnetic waves in an anisotropic medium? It is not obvious that the angular ...
3
votes
1answer
1k views

Chemical potential interpretation

Something that has bothered me for a while regards the interpretation of chemical potential for different statistics. While I understand its meaning in metals (and its relation with the Fermi ...
2
votes
0answers
358 views

A question about Dirac operator

The Dirac operator at 2 dimension can be written as $$ D=\sum_{k=1,2}\sigma^{k}D_{k}=\left( \begin{array}{cc} 0 & \partial_{x}-i\partial_{y}-i(A_x-iA_y)\\ ...
12
votes
3answers
1k views

Phonons in non-crystalline media

Do sound waves in a gas consist of phonons? What about a glass? Or other non-crystalline materials such as quasicrystals? How does the lack of translational symmetry affect the quantization of the ...
5
votes
2answers
552 views

effective theory of graphene

This is a question about deriving effective mass theory for graphene. For the two sub-lattice atoms, the wave equation can be written as the massless Dirac equation: $ \displaystyle -i\hbar v_F ...
8
votes
3answers
327 views

References on the physics of anyons

Anyone know some good introductory references on the physics of anyons?
2
votes
1answer
284 views

Axion related questions

I have several question regarding axion. Could anyone give me some brief introduction to what is a axion string, axion field and how is this related to fermion zero mode and chiral zero mode?
1
vote
0answers
424 views

Fermi level in disordered amorphous and/or organic semiconductors

So, the Fermi level in crystals is pretty easy to understand. Been using it and talking about it in terms of the highest occupied level forever. However, I'm now reading about disordered systems. A ...
15
votes
4answers
3k views

Quantum Hall effect for dummies

In the past few days I've become increasingly intrigued by the QHE, mainly thanks to very interesting questions and answers that have appeared here. Unfortunately, I am as of yet very confused by all ...
4
votes
1answer
376 views

Relationship between magnetic resonance linewidth and spin relaxation

First of all, what is the mathematical relationship between measured linewidth (usually in units of magnetic field) and spin relaxation time? I see papers talk about spin relaxation times in terms of ...
5
votes
2answers
772 views

How much can AdS/CMT tell us?

I will begin my research on AdS/CMT, however I find AdS/CMT is only a phenomelogical method, so I want to know can AdS/CMT give some results the condensed matter physicists can not give, or even ...
4
votes
1answer
1k views

1D topological insulator

This question is inspired by another one about the simplest model of topological insulator, where 4tnemele showed a nice two band model in the answer. I read that and am wondering if we and push that ...
5
votes
1answer
417 views

What is the boundary condition of graphene flake with zigzag edges?

It is a question about free carrier behavior in graphene flakes. (or may be called charge confinement) Say if we have a perfect hexagonal free standing graphene flake terminated with zigzag edges. ...
12
votes
3answers
330 views

Why are so many condensed matter phenomena so dependent upon impurities?

Why are so many condensed matter phenomena so sensitive to impurities? In fact, quite a number of them depend upon impurities for their very existence!
7
votes
4answers
4k views

What is Fermi surface and why is this concept so useful in metals research?

What is Fermi surface and why is this concept so useful in metals research? Particularly, I can somewhat appreciate the Fermi energy idea - the radius of Fermi surface which is a sphere. But is there ...
-2
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1answer
343 views

Are strange metals described by a quantum critical theory?

Are strange metals described by a quantum critical theory?
3
votes
2answers
419 views

On-site repulsion and Pauli exclusion

Been studying hopping conduction and something that everyone is taking for granted is bothering me. Let's say we have a bunch of sites that are either unoccupied, singly occupied, or doubly occupied. ...
3
votes
1answer
654 views

Energy levels in disordered organic semiconductors?

Now in disordered organics, the band picture is thrown out the window, from what I can tell (due to lack of symmetry). But don't HOMO/LUMO levels basically take the place of conduction/valence bands ...
4
votes
1answer
1k views

Do derivatives anticommute with Grassmann variables and complex numbers in a many-body path integral?

I'm trying to learn how to do a many-body path integral for both fermions and bosons, and I'm stuck. I'm following Altland and Simons - Condensed Matter Field Theory, chapter 4. On page 167, equation ...
12
votes
3answers
2k views

trying to understand Bose-Einstein Condensate (BEC)

I am a computer scientist interested in network theory. I have come across the Bose-Einstein Condensate (BEC) because of its connections to complex networks. What I know about condensation is the ...
9
votes
4answers
2k views

Bose-Einstein condensate in 1D

I've read that for a Bose-Einstein gas in 1D there's no condensation. Why this happenes? How can I prove that?
18
votes
5answers
5k views

What does it mean for a Hamiltonian or system to be gapped or gapless?

I've read some papers recently that talk about gapped Hamiltonians or gapless systems, but what does it mean? Edit: Is an XX spin chain in a magnetic field gapped? Why or why not?
0
votes
2answers
450 views

Matter in superconductive state [closed]

We distinguish between the states of matter: gas, liquid and solid. Possibly we could add the plasma state and/or the superconductive state as new states of matter. Phase transistions at certain ...
2
votes
2answers
240 views

existing bounds on maximum density achieved by a Bose condensate

As we know, fermions are subject to exchange interactions that limit the densities they can achieve. However bosons (simple or composite) are not constrained by this, which implies physical phenomena ...
2
votes
1answer
766 views

What is the mechanism of dielectric saturation?

It is known from experiments that the dielectric constant of a solvent might decrease in regions where there is a strong electric field, for example, near a highly charged ion in an infinitely dilute ...
7
votes
1answer
352 views

How many stabilised qubits have been achieved in Quantum Computing?

The latest I read is 3 but that was in Oct. With Lene Hau of Harvard's "frozen light" and with quantum donuts, newer strategies for stabilization are appearing, but the problem of keeping the qubit in ...
0
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1answer
304 views

Volume of Matter in the Universe [closed]

What would the size of the universe be if it were physically possible to remove all of the empty space, leaving only matter?
8
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1answer
311 views

Resistance of a two-dimensional sample

In this review of the QHE, Steve Girvin makes the following statement (bottom of pg. 6, beginning of Sec. 1.1.1): As one learns in the study of scaling in the localization transition, resistivity ...
8
votes
2answers
1k views

How do Dirac fermions arise in graphene, and, what significance (if any) does this have for high-energy physics?

Graphene has a honeycomb lattice (in the absence of defects and impurities). By considering the low-energy limit of the half-filled Hubbard model used to model the strongly interacting electron gas we ...
20
votes
5answers
3k views

Simple models that exhibit topological phase transitions

There are a number of physical systems with phases described by topologically protected invariants (fractional quantum Hall, topological insulators) but what are the simplest mathematical models that ...