科研之友
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摘要
Several years after Kim and Chan's discovery of an anomaly in the rotation properties of solid helium (Kim and Chan in Nature 427:225, 2004; Science 305:1941, 2004), the interpretation of the observed phenomena as a manifestation of supersolidity remains controversial. J. Beamish and his collaborators have shown that the rotation anomaly is accompanied by an elastic anomaly (Day and Beamish in Nature 450:853, 2007; Day et al. in Phys. Rev. Lett. 104:075302, 2010; Syshchenko et al. in Phys. Rev. Lett. 104:195301, 2010): when the rotational inertia apparently increases, the shear modulus decreases. This softening is due to the appearance, in the solid, of a large reversible plasticity that is a consequence of the evaporation of He-3 impurities from dislocations that become mobile. This plasticity is called "quantum plasticity" because the dislocations move by quantum tunneling in the low temperature 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 stiffness of solid He-4, it is not totally clear if supersolidity really induces a change in inertia or if it is the disappearance of quantum plasticity that mimics supersolidity in TO experiments. In order to distinguish between supersolidity and quantum plasticity, we have studied the rotational and the acoustic properties of solid He-4 samples with a variable amount of disorder and of He-3 impurities. Of particular interest is the comparison of single crystals to polycrystals but the whole problem is not yet solved. This short review article is an opportunity to discuss several questions regarding the exact role of disorder in supersolidity and in quantum plasticity.
- 出版日期2012-8
