# Tagged Questions

2answers
135 views
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### 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 ...
3answers
169 views

### There must be free positive charges, moving oppositely to electrons for the wire with current to stay neutral

All popular expositions (e.g. these ones) of relativistic electromagnetism claim univocally that electrons in motion become more dense due to the speed. They teach that Lorentz contraction of charges ...
1answer
43 views

### Understanding drift velocities in currents

I have a doubt about the understanding of drift velocities in a current. My problem is that the textbook speaks very loosely about this. It's like: "well, if we apply a field $E$ then the charges will ...
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 ...
3answers
253 views

### Why is copper diamagnetic?

Cu has an unpaired electron in 4s, but it is diamagnetic. I thought that it has to be paramagnetic. What am I missing?
2answers
349 views

### What is the difference between a photon and a phonon?

More specifically, how does a wave-particle duality differ from a quasiparticle/collective excitation? What makes a photon a gauge boson and a phonon a Nambu–Goldstone boson?
0answers
41 views

### Order of magnetic phase transitions

Is there any phase transition occur in paramagnetism to diamagnetism transitions state. What should be the order and how will I calculate the order?
1answer
901 views

### Why are some materials diamagnetic, others paramagnetic, and others ferromagnetic?

Why are some materials diamagnetic, others paramagnetic, and others ferromagnetic? Or, put another way, which of their atomic properties determines which of the three forms of magnetism (if at all) ...
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 ...
1answer
267 views

### Pull up and Pull down register

Currently I am working with Pull up and pull down registers and trying to understand what does it mean? But could not able to understand. I searched in Wikipedia ...
1answer
164 views

### What is the time correlation function in the Green-Kubo formulation of ionic current?

I am reading a paper, and I came across the Green-Kubo formulation, where the conductivity $\sigma$ of charged particles is related to the time correlation function of the $z$-component of the ...
2answers
90 views

### What are the specific electronic properties that make an atom ferromagnetic versus simply paramagnetic?

As I understand it, paramagnetism is similar in its short-term effect to ferromagnetism (spins of the electrons line up with the magnetic field, etc.), though apparently the effect is weaker. What is ...
1answer
240 views

### Lorentz invariance of a frequency- and wavelength- dependent dielectric tensor

Suppose we have a material described by a dielectric tensor $\bar{\epsilon}$. In frequency domain, this tensor depends on the wave frequency $\omega$ and the wave vector $\vec{k}$. Clearly not all ...
3answers
560 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 ...
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