More MM07

More good physics at the APS meeting, though I'm rapidly approaching the point of mental exhaustion.

There was an invited symposium on silicon nanoelectronics on Wednesday that was very nice - I only saw the first three talks, but they were all good. Steve Lyon from Princeton spoke about his ESR measurements on small numbers of electrons in Si/SiGe heterostructures and dots. Mark Eriksson from Wisconsin gave a good overview of their recent work on trying to get gate-defined quantum dots in Si/SiGe to act as nicely as those in GaAs/AlGaAs. A main point of physics in both of those talks was the effect of valley degeneracy on spin physics in those structures. In bulk Si the bottom of the conduction band is 6-fold degenerate and not located at k=0. In quantum wells or heterojunctions, the degeneracy is partially lifted due to the broken spatial symmetry. Mark and Steve have both been worrying about the size of the splitting in energy between the lowest valley and the next valley, and Mark's work looks like it answers the question in gate-defined dots. The third talk was by my old friend Sven Rogge now from Delft. There he has been working on making measurements on states confined to individual dopant atoms in ultrasmall Si transistors. It's extremely interesting to look at how the hydrogen-like donor wavefunctions hybridize with Si well states when the gate field pulls the electron from the donor toward the well.

Today I've seen two very smooth talks in nanostructures sessions. In the first Amir Yacoby, late of the Weizmann Institute and now at Harvard, showed new work on transport through "double dot" structures made from two metal nanoparticles linked by a small organic molecule. At low temperatures and voltages, the physics is dominated by Coulomb charging effects of the two nanoparticles. They see all kinds of rich Coulomb blockade behavior that can be modeled basically perfectly with only a few free parameters (the capacitances and resistances of the relevant junctions). The second was a talk by Lars Samuelson at Lund. He's one of the big movers and shakers in growing semiconductor nanowires. He gave a full overview of their work on this, which has included some obscene number of high impact publications. People with that kind of productivity are simultaneously impressive and depressing.

Incoherent Ponderer is absolutely right about the graphene thing. I've heard some nanotube folks griping that graphene is the new hotness.