1
vote
0answers
40 views

Debye Hückel Theory valid for ions?

I am wondering about the following: Is Debye Hückel Theory only used if you look at how an external "strong" field(like a potential by a sphere that has a charge that is 1000times higher than the ...
1
vote
3answers
139 views

Why are free electrons free?

This is what I understand so far: in a conductor, the ions have a weak pull on the valence electrons. So when an electric field is applied, the free electrons are able to easily move about. Makes ...
3
votes
2answers
103 views

How to derive the Aharanov-Bohm effect result?

In the derivations of the Aharonov-Bohm phase, it is directly mentioned that due to the introduction of the vector potential $A$, an extra phase is introduced into the wavefunction for case $A\neq0$ ...
1
vote
0answers
46 views

Electron-electron interaction in solids

We always consider a Coulomb interactions between electrons in the Hamiltonian to modelize a solid. Why not to take into account retardation effects of the electromagnetic interaction which go beyond ...
0
votes
1answer
74 views

What happens when molten metal cools within a strong magnetic field?

What happens when molten metal cools within a strong magnetic field? I don't know what more say, don't remember anything relevant to this in my uni text books.
1
vote
2answers
128 views

Derivation of Lagrangian density for an infinite classical dielectric in interaction with the EM field

I am tasked with reading and reproducing all the steps in J.J. Hopfield's 1958 paper "Theory of the Contribution of Excitons to the Complex Dielectric Constant of Crystals". Embarrassingly I am stuck ...
0
votes
1answer
71 views

Why is an optical magnon with k=0 not an eigenenergy state?

I found in a paper the following explanation. Unfortunately, I can't understand it. Can anyone help me on this? In the limit of equal spins an optical magnon with k=0 gets an acoustical one at the ...
1
vote
0answers
54 views

Long range repulsion in anomalous solids

As far as I know things like rocks, walls, rubber balls, polished tables etc. exert a short range repulsive force on other everyday objects that is responsible for hardness, softness, collisions, ...
0
votes
0answers
37 views

Anisotropy and demagnetizing field

I'm trying to calculate the anisotropy constant of a ferromagnetic material. Then, of course, I need to worry about the demagnetizing field. However, a book I'm reading claims that we can calculate ...
0
votes
0answers
62 views

What is the physical property of metal nanoparticles?

I am a Math student but now I have to deal with gold nanoparticles in aqueous solution. Now I was wondering whether the physical properties of gold nanoparticles are the same as the properties of gold ...
1
vote
1answer
129 views

Accelerated charged particles produce electromagnetic radiation, but holes (the charge carriers) do not. Is this correct?

Holes are treated as particles in solid-state physics, so I've had some trouble with reasoning through this properly.
9
votes
2answers
229 views

Ferromagnetism with mobile spins

How can electron spins in Iron at room temperature have ferromagnetic order even though they are travelling at very high speeds? One could argue that spin and motion are completely uncorrelated and ...
1
vote
2answers
113 views

Free spin (Curie) Paramagnetism

I'm working through a derivation for Curie paramagnetism and hope someone could help clarify a couple of steps. The way that makes sense to me (although now I have seen the wikipedia derivation below ...
3
votes
1answer
229 views

Fermi level with Landau levels

So my question is regarding where the Fermi energy is when you have 2D electron gas in an applied magnetic field. My book explains that, using the Landau gauge, you find that the 2D density of states ...
2
votes
1answer
41 views

Does an Ising lattice that returns to equilibrium create a current by induction?

Consider you have an Ising lattice with a dominant up component out of thermal equilibrium, that's your initial state. The down spins want to flip up and align with the ups, and they'll do so until a ...
3
votes
1answer
115 views

Question about Classical Transport Theory

With a distribution function of the form $f=f_{0} + \vec{v} \cdot \vec{g}$, one can obtain the current density. My question is about $\vec{g}$; we assume a general solution to $\vec{g}$ of the form ...
2
votes
1answer
2k views

Optical constants of noble metals: the Drude model for microwave modelling

I have a question regarding the optical constants of noble metals. According to Johnson and Christy's paper Optical Constants of Noble Metals (Phys. Rev. B 6, 4370–4379 (1972), ...
4
votes
1answer
2k views

Physical meaning of magnetic length

What is the physical meaning of magnetic length $\ell_B=\frac{\hbar c}{e B}$ in 2D electron system under magnetic field? When $\ell_B \longrightarrow a$, where $a$ is the lattice constant, does that ...
2
votes
0answers
119 views

Where can I find a complete list of metamaterials up to today?

Where might I find a list of all the metamaterials up-to-date?
3
votes
2answers
68 views

heavy nuclei surface exposed to positron gas

Suppose there is a material with heavy nuclei attached on its surface, presumably binded by the outer shell electrons. Now, the surface is exposed to a cold positron gas, which annihilates against ...
2
votes
1answer
215 views

What is nonlocal resistance?

We are first taught to calculate local resistance, where current and voltage are on the same part of the material. But many experiments measure nonlocal resistance, where current and voltage are ...
2
votes
1answer
122 views

Crystal magnetic response only skin deep?

The Hamiltonian for a single electron in a magnetic field reads $$H=\left(\frac{{\bf p}^{2}}{2m_{e}}+q_{e}\phi\right)+\mu_{B}\left({\bf \hat{L}}+g{\bf \hat{S}}\right)\cdot{\bf ...
6
votes
2answers
528 views

Can water be magnetized?

This may be a stupid question, so feel free to shoot it down. Assuming all atoms have a magnetic moment, I would assume the water molecule too would have a resultant magnetic moment; ergo, it may be ...
6
votes
0answers
206 views

Can I integrate out the fermion field that is not gapped?

This piece of argument has been repeated again and again by experts, that is Since the fermions are gapped, then I can integrate it out. but I have no idea of what will happen if the fermions ...
2
votes
3answers
424 views

Gauge invariance and form of the vacuum polarization tensor

In quantum field theory or condensed matter physics, the fermionic one-loop diagram gives rise to the polarization tensor $$ Π^{µν} = Tr[ γ^µ G γ^ν G ] $$ If we couple the electrons to an ...
2
votes
1answer
885 views

Which ferromagnetic material has the lowest Curie temperature?

It is hard to search for materials by their properties in general and I am trying to find a material with a very low Curie temperature. At the moment I am browsing different sites but can only find a ...
4
votes
2answers
423 views

Why do physicists believe protons and electrons are present in equal numbers?

I tended to consider that negative and positive charges are present in equal numbers in the universe to be a known, obvious fact. But is it so? How can we rule out the possibility that there is some ...
8
votes
2answers
5k views

How does quantum trapping with diamagnets work?

I just saw this demonstration by someone from a Tel Aviv University lab. What they achieved there is mind blowing. I myself own a levitron that uses the Hall effect to levitate a magnet, the problem ...
2
votes
1answer
121 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? ...
5
votes
1answer
203 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 ...
4
votes
1answer
317 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 ...
12
votes
3answers
795 views

Shine a light into a superconductor

A type-I superconductor can expel almost all magnetic flux (below some critical value $H_c$) from its interior when superconducting. Light as we know is an electromagnetic wave. So what would happen ...
12
votes
1answer
4k views

Kubo Formula for Quantum Hall Effect

I'm trying to understand the Kubo Formula for the electrical conductivity in the context of the Quantum Hall Effect. My problem is that several papers, for instance the famous TKNN (1982) paper, or ...