Disorder, Supersolidity, and Quantum Plasticity in Solid Helium 4

Abstract

Abstract Several years after Kim and Chan’s discovery of an anomaly in the ro-tation properties of solid helium (Kim and Chan in Nature 427:225, 2004; Science305:1941, 2004), the interpretation of the observed phenomena as a manifestationof supersolidity remains controversial. J. Beamish and his collaborators have shownthat the rotation anomaly is accompanied by an elastic anomaly (Day and Beamish inNature 450:853, 2007; Day et al. in Phys. Rev. Lett. 104:075302, 2010; Syshchenkoet al. in Phys. Rev. Lett. 104:195301, 2010): when the rotational inertia apparentlyincreases, the shear modulus decreases. This softening is due to the appearance, in thesolid, of a large reversible plasticity that is a consequence of the evaporation of 3 Heimpurities from dislocations that become mobile. This plasticity is called “quantumplasticity” because the dislocations move by quantum tunneling in the low tempera-ture limit.Since the main evidence for supersolidity comes from torsional oscillator (TO)experiments, and since the TO period depends on both the inertia and the stiffnessof solid