# Search results

1. ### Derivation of LLG equation in polar coordinates

Can you be more specific about where you are having a hard time? Is it the change of coordinate system? Also, when asking a question like this, it's quite reasonable to mention that you're setting h_p=h=h_s=0. Makes it easier to relate your equations to those in the paper.
2. ### Band structure of cobalt adsorbed graphene

Well, I'm not sure how sensitive DFT is to these things or how the specific material is supposed to behave, but in other simulations one often needs to pay attention to boundary conditions (you can check if you have an even-odd effect when changing cell size) and to finite size effects. For the...
3. ### Most modern Solid State Model

The main issue with your first question is that there isn't really such a model. Or rather, one can only write something like H_{tot}=H_e + H_I + H_{int} where H_{tot} is the total Hamiltonian, H_{e} is the electron Hamiltonian which contains the kinetic energy of each electron and all...
4. ### What does an 2H- in front of a chemical symbol mean? (i.e. 2H-MoX_2)

Yeah, it has to do with stacking. There are several notations, of which I'm most used the ABC one myself. However, I think this is Ramsdell notation, in which H=hexagonal and the number two would signify the number of layers. Hence 2H should correspond to AB stacking, which agrees with the...
5. ### Ising model for spins

The average \langle S_j^z \rangle is certainly changed by the external magnetic field - consider the extreme case with an antiferromagnetic J and a strong field along some axis. This will change the mean field from zero in the case of no field to its maximal value in the case of a strong field...
6. ### Ising model, same interaction with all spins

I believe this tends to be called the "Ising model on a complete graph". See chapter 3 in these lecture notes. Since the atomic orbitals tend to be quite localized (few papers even consider next next nearest neighbor interactions) this case tends to be more popular in mathematics (judging by...
7. ### Electron beam litography

If you are asking about the technique rather than the detailed physical processes, note that photolithography works essentially the same way, but is usually much better explained. That wikipedia page illustrates it quite nicely with that figure. Electron beam lithography uses some other...
8. ### Properties of the Dirac point and Topological Insulators

The surface states tend to have them though, see e.g. Joel Moore's article. I am also not quite sure what the question is actually about. If the Fermi energy is at (or close to) the Dirac point, then the low-energy states will have a linear dispersion relation. This is a clear signal, and quite...
9. ### Is the energy density normalized differently in the quantum case?

Actually, the author of those notes probably just switched to a complex field E_V=\sqrt{\frac{\epsilon_0}{2}}E + i\frac{B}{\sqrt{2\mu_0}} in which case the energy density comes out as u=\int |E_V|^2 d^3 r = \int \left( \frac{\epsilon_0}{2}E^2 + \frac{B^2}{2\mu_0} \right) d^3 r as it should.
10. ### Is the energy density normalized differently in the quantum case?

Hi all, This is all in the context of interaction between (two-level) atoms and an electromagnetic field, basically the Wigner-Weisskopf model. In particular, I tried to derive the value of the atom-field interaction constant and show that it satisfied...
11. ### Van Hove singularity for a two dimensional lattice

By the way, I don't know why I dragged up the whole even function bit. That doesn't really help. I see. Yeah, I'm not sure about how to do that. But didn't we use dE=\nabla E \cdot \mathbf{k} to remove one of the momentum dimensions already? That kind of suggests that it might be simplest to...
12. ### Van Hove singularity for a two dimensional lattice

Ah, ok. Yeah, that Taylor series (unless you do the full infinite sum, in which case you wouldn't lose information) is mainly useful near the origin. But the other solutions are for k_x =\pm \pi/a, right? And |\nabla \epsilon| is an even function, isn't it?
13. ### Van Hove singularity for a two dimensional lattice

Do you mean |\nabla \epsilon|\simeq0? Then it seems to me that you could try a Taylor series.
14. ### Confused with notation

Yeah, it doesn't make sense if you think of i,j as vectors. The upshot is that you don't have to - the indices are just supposed to label all sites. As long as your system has finite length, width, height (and so on, if you want to) - all you need is one number. It doesn't need to have anything...
15. ### Confused with notation

So what do you get if you write out the first sum? Hint: Your second Hamiltonian only has nearest neighbors.
16. ### Has Luttinger liquid been experimentally confirmed?

For your and others' future reference, this review on the experimental status of the Luttinger liquids was posted on arXiv yesterday: http://arxiv.org/abs/1308.2731 The review is relatively short, but Giamarchi (the author) covers more tests than I was aware of anyway, and provides references...
17. ### Hydrogen isotopes in palladium

Yes, there are no electronic differences between isotopes. The chemical difference is due to the increased mass, making reactions and transport slower. (This effect becomes negligible for heavier elements, by the way.) Practically speaking, isotopes above tritium have too short half-lives to be...
18. ### Lande g factor

I haven't seen it outside that book or the article by Lamb they cite, but then again, it does seem like the kind of detail any book except for Bethe & Salpeter would hide under the rug. Except for the case of Hydrogen and possibly Helium, it really is a small effect. Did you read the...
19. ### Has Luttinger liquid been experimentally confirmed?

What would you consider a definite proof? The Luttinger liquid does a good job for e.g. carbon nanotubes and edge states of fractional quantum Hall systems, but it is a linearised theory which can only deal with low energy excitations. As it is a limit, there will clearly be cases when it does...
20. ### Why symmetry breaking a paradigm whilst not describing Fermi liquid?

Is your question whether the Fermi liquid is a state with an order different from the Fermi gas, or whether you can have phase transitions in the Fermi liquid? If it is the latter, then yes, you can have instabilities that lead to magnetic ordering or pairing. If it is the first, I think the...
21. ### P orbital notation

Ah! Now that makes some sense. Thank you.
22. ### P orbital notation

Here it is, I hope...
23. ### P orbital notation

Hi, Reading http://rmp.aps.org/abstract/RMP/v70/i4/p1039_1 I've run into a notational question of atomic p orbitals. The authors use symbols like p_\sigma and p_\pi. From their fig. 3 (attached), they do look like p_x and p_z orbitals, respectively, rather than anything close to σ or π bonds...
24. ### Rashba effect due to the external electric field

Where does it say that? That is quite misleading. Basically, one can use the traditional hand waving argument: a travelling electron will perceive electric fields as magnetic fields (which the electron spin can couple to). In the simplest case, a lone Hydrogen atom, the field is entirely due...
25. ### NIST Atomic Spectra Database

See http://physics.nist.gov/PhysRefData/ASD/Html/lineshelp.html#OUTWAVELENGTH The Ritz wavelengths are calculated from the difference in the energy levels involved in the transition, whereas the observed values are the experimental data. The accuracy of the Ritz wavelengths obviously depends...
26. ### Why isn't spin a 5th dimension?

The spin vector (if we allow ourselves to use the semi-classical picture, in which spin forms a vector) has a fixed lenght for any particle (that is, the electron spin 1/2 doesn't change), so it's not really a dimension in that (infinite) sense. You could add a number of "spin dimensions" equal...