SCES '07 day 4

Back to the SCES conference this afternoon, after my campus commitments, for the second session on strong correlations in mesoscopic systems. Some highlights:

David Goldhaber-Gordon gave a nice talk about his group's work on using semiconductor nanostructures to engineer the two-channel Kondo effect. The work has been published here and is available on the arxiv here. In the single-channel Kondo problem, a free spin is coupled via tunneling to a single electronic bath. Antiferromagnetic exchange between the spin and the conduction electrons leads to the formation of a singlet at low temperatures - the spin is screened, and the ground state of the system is a Fermi liquid. In the two-channel Kondo problem, a single spin is coupled via tunneling to two independent electronic baths. Each bath tries to "screen" the spin via antiferromagnetic exchange, with the result that the spin is overscreened. The ground state of that system is supposed to be a non-Fermi-liquid, meaning that its low energy excitations don't look like weakly interacting quasiparticles. The hard part about testing this is actually making two truly independent electronic baths. The paper shows a clever implementation that effectively does this, at least over a limited temperature range.

Yong Chen, one of Randy Hulet's postdocs, gave a talk about using cold atoms to study Anderson localization. By sending a laser through frosted glass, they can use the resulting speckle pattern to provide a disordered potential for trapped cold bosonic atoms. They can dial around the strength of the disorder potential by changing that laser's intensity. Then they can play games with the trap potential to test how delocalized the Bose-condensed atoms are (kick the trap and look for resulting oscillations), and independently check for coherence by looking for interference fringes. The preliminary data are pretty exciting.

Ravin Bhatt talked about (theoretical) ways to try and produce ferromagnetism in doped semiconductors containing only nonmagnetic atoms, at very low carrier densities. The trick is to somehow get the system to have more electrons than there are donors. One can imagine doing this with clever modulation doping schemes. No one's pulled it off yet, but it sounds cool and the numerical results look suggestive.

Unfortunately more Rice commitments mean that I won't make it to the last day of the conference tomorrow. Ahh well. It was an interesting meeting.