Sunday, March 30, 2008

A nice piece of physics with an elegant consequence

Kuzmenko et al. from Geneva have a PRL out this week titled "Universal Optical Conductance of Graphite". This is a pretty physics result, where the authors find theoretically and demonstrate experimentally that the optical conductivity of graphite is quantized - each graphene sheet has, at optical frequencies, a sheet conductance that is (\pi/2) e2/h. This is a consequence of the particular band structure of graphene, and I think it's rather impressive that this is robust even when there are multiple graphene layers. You might imagine, a priori, that the interlayer coupling would kill this kind of universality.

Nair et al., in a preprint, arrive at essentially the same result, but present the data in a much more dramatic way that does a great job of emphasizing the consequences of the physics. Many people don't have a good intuition for what optical conductivity means. Nearly everyone, though, has a decent sense of what optical absorption means. These folks demonstrate that the quantized optical conductivity implies that the white light absorption of graphite is quantized (!) in units of the fine structure constant (!!), so that each additional graphene layer absorbs 2.3% of the light incident on it, even though each layer is just one atom thick. The figures in the paper, particularly the last one, do a great job of making this point.

The take-home message about presentation: having a compelling physics story to tell is good, and casting it in terms that a general audience can appreciate with some intuition is even better.


Luiz Sampaio said...

PRL reference is not working.

Douglas Natelson said...

Fixed. Thanks. That's the first time in a while that the DOI link has failed me.

Anonymous said...

" optical adsorption "

do you mean optical absorption?

Douglas Natelson said...

Yes. Typo fixed.

Anonymous said...

Huh, I wonder if the quantized optical absorption could be the basis for a new standard? Would an absorption standard be useful?