why do periodic lattices conduct better

DrDu

Even a perfect crystal will have finite conductivity due to electron electron and electron phonon Umklapp scattering.
For AC at near the plasma frequency, an important mechanism for resistance are interband transitions.

Minich

It can't be right at all!!!

We consider quite common topic: friction!

For electron gas in solids it is named as resistivity.
For helium 3 and 4 it is named as viscosity.

And what do we see?
Even for IMPERFECT solids and for more IMPERFECT liquids there is SUPERCONDUCTIVITY and SUPERFLUIDITY.
There is NO microscopic theory of superfluid helium and of high temperature superconductivity. Some physicists suppose that also BCS theory can't explain some evident EXPERIMENTAL facts (for example Chapnik Kikoin rule, that most of elemental superconductor have pozitive Hall coefficient

).

So the question: what is it friction ( resistivity/viscosity), does not have clear MICROSCOPIC answer till now.

Gobil

really? there is no microscopic theory of superconductivity at high temperatures?

Aside from that, I just wanted a kind of idea of the mechanism for light absorption in metals. Particularly at wavelengths above the plasma frequency, I guess there are inter band transitions going on in the conduction bad right? but is the absotpion happening because the light is shaking the electron and the electron is colliding with an imperfection or a phonon, or another electron?
are all these processes happening?
What about at 0K?

thanks!

DrDu

Well, I would say that this is quite a particular oppinion of Minich whose paper on that topic we all are awaiting eagerly. Also note that he refers more to superconductivity and superfluidity than to resistance in ordinary metals at higher temperatures.

Minich

For current state of microscopic theory of superconductivity at high temperatures i can advice the exellent review of Uchida
Forefront in the Elucidation of the Mechanism of High-Temperature Superconductivity
Shin-ichi Uchida
Department of Physics, University of Tokyo, Bunkyo, Tokyo 113-0033, Japan
Received August 4, 2011; accepted September 8, 2011; published online December 7, 2011
It is only 5 pages.
Can be downloaded from
http://jjap.jsap.jp/journal/JJAP-51-1R.html
OR with free YELLOW comments from Minich can be download from
http://frolih.narod.ru/

I don't think that Uchida knows particular opinion of Minich. I think Uchida doesn't know that any "minich" exists :)

The first sentence from abstract:
So it is not my particular opinion that there is no microscopic theory of superconductivity at high temperatures :)

I will express my particular opinion in another post.

DrDu

Yes, I agree that on HTSC we have no theory (or far too many). The sentence I really wante to object was the following:

"So the question: what is it friction ( resistivity/viscosity), does not have clear MICROSCOPIC answer till now."
I would say that we have a good understanding of how resistivity arises in most substances. although there are always substances where special mechanisms are at work that are not well understood.

Minich

Let us see a solid at 0K. There is a ground state of a solid. When photon strikes a solid there are many channels to get solid in another (usually excited) state. So do photon's final states and electron(s) final states knocked out from the solid. The final state of the solid is not usually the stationary state of the solid and this state has probabilistic time evolution. Usually the solid is in contacts with many external sources of material world (other solids, electromagnetic fields and so on).

Such contacts as a rule are considered to obey probability rules. It means we name
such behavior as dissipation. For solids usually we have thermalisation processes.

If a solid has impurities the time evolution of the excited solid (as a whole) differs from that of excited solid without imputities.

At 0K we have no phonons.

There are too many possibilities.

Minich

Yes, You are quite right!

P.S.
As for Uchida review
Forefront in the Elucidation of the Mechanism of High-Temperature Superconductivity - Shin-ichi Uchida - COMPREHENSIVE REVIEW
I found, that Uchida has genius intuition.
He expressed one of the method to increase Tc with the help of pseudogap!
I am going to show how it can be achieved in my paper :)
Pseudogap insulator we can force to superconduct combining with overdoped superconductors at T near to pseudogap T* transition.
You can see the paragraph on page 4 near his reference to number 17:
17) S. Ideta, K. Takashima, M. Hashimoto, T. Yoshida, A. Fujimori, H. Anzai,
T. Fujita, Y. Nakashima, A. Ino, M. Arita, H. Namatame, M. Taniguchi, K.
Ono, M. Kubota, D. H. Lu, Z.-X. Shen, K. M. Kojima, and S. Uchida:
Phys. Rev. Lett. 104 (2010) 227001.