Van der Waals-Zeeman Colloquium
Thursday, 16 Oct 2007, 16:00h
Supersolidity and disorder
Prof. Sebastien Balibar
Laboratoire de Physique Statistique, Ecole Normale Supérieure, Paris (France)
Supersolidity is the possible coexistence of superfluidity and crystalline order, a rather paradoxical phenomenon. Although it was proposed nearly 40 years ago by Andreev and Lifshitz (1969), Chester (1969) and Leggett (1970) that 4He crystals could be supersolid, it is not until the 2004 experiments by Kim and Chan (Penn State University) that experimental evidence for supersolidity was presented in solid helium. However, it appeared 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. 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 2D quantum systems. We have shown that they are not sufficient to explain supersolidity in all experiments. I will summarize the present understanding of this controversial issue.
 S. Sasaki, R. Ishiguro, F. Caupin, H.J. Maris, and S. Balibar, Science 313, 1098 (2006).
 S. Sasaki, F. Caupin, and S. Balibar, submitted to Phys. Rev. Lett. (July 2007)