[Pw_forum] Semi-Metallic behavior in semi-conductor superlattice;

[mkondrin]

On 07.04.2016 08:56, Zahra Taghipour wrote:
> Dear Developers and Users,
>
> I have a conceptual question:
> I am working on a semi-conductor superlattice that has an experimental Gamma-to-Gamma transition of 280 meV.
> On the other hand, I am trying to simulate this structure within DFT using QE to study the excitons (to be corrected with GW).
> What I see is a semi-metalic behavior: highest occupied is at Gamma, and lowest unoccupied is at the border of BZ and lower than highest occupied at Gamma. This behavior is seen for couple of different PP’s.
Hi!

This is not semimetal, but true metal. Holes in the Gamma-point and 
electron pockets at BZ borders.
> GW corrects Gamma-to-Gamma transition pretty well, which it is very close to the experiment; But, the semimetal behavior is still present.
If pockets still persist that means that there is something wrong with 
your superlattice. May be its period is larger than you assume (used in 
your model).
> So, here is my question:
>
> Lets’ say the Temperature is low. Experimentally, one excites the electron at Gamma (correct?),
No. Fermi level in your case will be below valence band top at Gamma point.
> therefore, how one sees the semi-metal effect in the experiment (Where does the fact that there is a k-point in the border that has lower unoccupied state than the highest Gamma show itself in the experiment?
Hall effect -> effective charge of carriers and carriers concentration. 
In fact you would see metallic conductivity in the case you have just 
described.

Hope this helps,
M.V.Kondrin
High Pressure Physics Institute RAS