6
votes
2answers
147 views
+50
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
37 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
96 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
37 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
94 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 ...
4
votes
1answer
295 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 ...
3
votes
2answers
61 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
113 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
115 views
Crystal magnetic response only skin deep?
The Hamiltonian for a single electron in a magnetic field reads
$$H=\left(\frac{{\bf p}^{2}}{2m_{e}}+q_{e}\phi\right)+\mu_{B}\left({\bf \hat{L}}+g{\bf \hat{S}}\right)\cdot{\bf ...
5
votes
0answers
144 views
Can I integrate out the fermion field that is not gapped?
This piece of argument has been repeated again and again by experts, that is
Since the fermions are gapped, then I can integrate it out.
but I have no idea of what will happen if the fermions ...
0
votes
0answers
32 views
Can one obtain saturation magnetization from FMR measurements?
Especially for magnetic thin films. Normally this is done by magneto-optical Kerr effect or SQUID measurements. Or is there a way to calculate the saturation magnetization based on other measured ...
2
votes
3answers
310 views
Gauge invariance and form of the vacuum polarization tensor
In quantum field theory or condensed matter physics, the fermionic one-loop diagram gives rise to the polarization tensor
$$ Π^{µν} = Tr[ γ^µ G γ^ν G ] $$
If we couple the electrons to an ...
2
votes
1answer
549 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
324 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 ...
2
votes
1answer
112 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
193 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
252 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
561 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 ...
7
votes
1answer
3k 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 ...
