Tuesday, February 26, 2008

This week in cond-mat

A brief look at three papers from the past week that I thought looked particularly interesting.

arxiv:0802.3236 - Bleszynski-Jayich et al., Imaging a 1-electron InAs quantum dot in an InAs/InP nanowire
For a number of years now the Westervelt group at Harvard has been at the forefront of using scanned probe microscopy to examine the electronic states in semiconductor nanostructures. The basic idea is simple: use a conducting AFM tip as a local gate, and measure the transport through the nanodevice as a function of the tip position. If the gate is located somewhere irrelevant to the current paths through the device, you see no effect. By mapping the device response to the gate, you can map out many interesting features in the electronic states that contribute to transport. This is another example of applying this basic technique, this time to one of the InAs-based structures that Lars Samuelson has been developing extensively in recent years. Very nice. The data are rather psychedelic.

arxiv:0802.2350 - Geraci et al., Improved constraints on non-Newtonian forces at 10 microns
These kinds of experiments are "small scale physics" at its best. The high energy theory community has been talking for a while about whether "large" extra dimensions (beyond the usual 3+1 of ordinary space-time) can show themselves through deviations in Newtonian gravity at the sub-mm scale. Measurements of G, the gravitational constant, at these distances are extremely challenging. Remember, electromagnetic forces can swamp gravity by 40 orders of magnitude, and there are all kinds of complications that can arise in such measurements. I always enjoy these experiments, where extreme skill and cleverness are used to go after big foundational questions without gigadollar particle accelerators.

arxiv:0802.3462 - Min et al., Room-temperature superfluidity in graphene bilayers?
There's an old saying that the answer to any rhetorical question in the title of a paper is always "no". Here, however, Allan MacDonald and company suggest the opposite. It would appear that the special properties of graphene's unusual band structure may lead to superfluidity of bilayer excitons (a hole in one layer bound electrostatically to an electron in the neighboring layer to form an effective composite boson that is overall charge-neutral) at room temperature. There's been evidence for a while of low-T excitonic superfluidity in 2d electron/hole bilayers. This would be very neat, and it's always nice to see theorists making provocative predictions. (It would not lead to room temperature superconductivity, though! Since the excitons are neutral, their superfluid state doesn't carry a net current.)

1 comment:

WebVisible said...

This would be very neat, and it's always nice to see theorists making provocative predictions.