This week in cond-mat

Two preprints that caught my eye this week:

cond-mat/0604528 - Elimination of the supersolid state through crystal annealing, Rittner et al.
This paper is the work of John Reppy's group at Cornell, and is part of a large effort going on by a number of people to verify or refute the observations of Moses Chan's group - that there's a "supersolid" state of helium (4He) under high pressure (tens of bars) and low temperatures (below 1 K). A supersolid is a solid that exhibits "nonclassical rotational inertia". Put another way, in a superfluid, the atoms in the system form a kind of condensate - a macroscopic quantum phase where all the atoms behave cooperatively. If the atoms are weakly interacting bosons, the system can be described as a Bose-Einstein condensate. In a supesolid, the vacancies in the crystal lattice are thought to undergo some kind of condensation into a single quantum phase. This new paper reproduces the results of Chan et al., and finds that the supersolid behavior in 4He crystals can be eliminated entirely by annealing the crystals near their melting point. It would appear that the disorder responsible for the supersolidity can be removed by annealing. Nice paper.


cond-mat/0605739 - Landau level spectroscopy of ultrathin graphite layers, Sadowski et al.
This paper shows some beautiful cyclotron resonance data taken on graphene sheets as a function of carrier density. As I've mentioned before, graphene is a very funky model system, in which the electrons and holes act just like (apparently) massless Dirac fermions, because of the peculiarities of the graphene band structure. This work is very pretty, and is a cool example of an experiment that, in some ways, is analogous to electron-positron pair production (!). I'm a big fan of solid state systems that are models of more general physics.