Disorder, Supersolidity, and Quantum Plasticity in Solid Helium 4 - Balibar, S. and Fefferman, A. D. and Haziot, A. and Rojas, X.
JOURNAL OF LOW TEMPERATURE PHYSICS 168, 221-234 (2012)
Abstract : 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
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
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