Thursday, October 15, 2009

Fractional Hall Effect Observed in Graphene

Graphene has become almost the "aspirin" of condensed matter, exhibiting everything from "speed of light" electron transport, and now, fractional quantum hall effect.

Andrei and her team have finally spotted electrons in graphene getting together in the right way. To do it, the team suspended micrometer-sized bits of graphene to avoid interference from the underlying substrate. The researchers then used a special arrangement of electrodes to keep from shorting out their own measurements, they report online this week in Nature. They observed quasiparticles with 1/3 an electron's charge. In fact, Andrei says, the researchers saw the effect at higher temperatures and lower magnetic fields than are needed to see it in semiconductors, suggesting that the electrons in graphene interact especially strongly.

This is turning out to be such an amazing material, as amazing, if not more, than the high-Tc superconductors.



Heumpje said...

One difference with the high Tc's, or most other materials, is that there we discover fundamental new states of matter, while in graphene everything gets predicted before it is observed. So graphene may be interesting for applications and a good playground for theoreticians, but that is not the same as saying that it will change our understanding of nature.

Anonymous said...

An issue I have with this work is they keep calling it the fractional quantum Hall EFFECT and yet it's a two-terminal measurement. There's a difference between the FQHE and a FQH state. I don't consider this measurement as a measurement of the FQHE since the FQHE, by definition I would think, is a plateau in the Hall resistance R_xy and a concomitant vanishing (as T approaches 0) of the longitudinal resistance R_xx. This two-terminal measurement does not independently measure these things. I think Andrei (and Philip Kim has seen FQHE in graphene too) should be claiming an observation of FQH STATES in graphene. Specifically, the 1/3 FQH state.

I know...I'm being anal retentive...but at least in principle they could be measuring a non-plateaued R_xy and a non-vanishing R_xx that are conspiring in just the right way to produce a plateau at 1/3. I know it's very very unlikely...but hey...this is physics and it's possible.