|Supersolidity and Disorder |
Physics and Astronomy
|Sebastian Balibar, ENS Laboratoire de Physique Statistique, Ecole Normale Superieure, Paris, France|
1:30 PM, Serin E385
Is it really possible that a solid flows without friction like a superfluid?
Although several theorists discussed nearly 40 years ago the possible existence of supersolids, that is solids which could be also superfluid, it is only in 2004 that Kim and Chan presented non-classical rotational properties of solid helium as a possible evidence for supersolidity. In 2007, evidence for anomalies in the elastic properties of helium crystals has also been presented by Day and Beamish.
The interpretation of these experiments leads to fundamental questions on localization of atoms in quantum solids. They triggered an intense controversy among both theorists and experimentalists, which I will try to summarize.
It appears in 2006 that disorder played a major role in the observed phenomenon. In particular, Rittner and Reppy(Cornell) showed that annealing helium crystals reduced the supersolid density by several orders of magnitude. But one has not yet understood which kind of disorder leads to the observed anomalies nor by which mechanism.
At the ENS in Paris, we showed that grain boundaries in polycrystalline samples allow mass superflow through solid Helium. The wetting properties of grain boundaries are important in materials science and we have started their study in solid He where they are interesting two-dimensional quantum systems. However, we have shown that their existence is not sufficient to explain supersolidity in all experiments.
I will conclude with a few perspectives for the near future of this paradoxical subject.
 S. Sasaki, R. Ishiguro, F. Caupin, H.J. Maris, and S. Balibar, Science 313, 1098 (2006).
 S. Sasaki, F. Caupin, and S. Balibar, Phys. Rev. Lett. 99, 205302 (2007)