Phenomenological Ginzburg-Landau theory for supersolidity

Abstract

A Ginzburg-Landau theory is proposed in which the supersolid state is viewed as a system displaying features of an ordinary solid and of a superfluid. The theory shows that the superfluid part is responsible for a nonclassical rotational inertia (NCRI) behavior, but the ordinary part (the lattice) is responsible for elastic behaviors usually seen in solids. Moreover, the superfluid part contributes to an excess of heat capacity near the supersolid--ordinary solid transition. The theory provides a coherent picture, at least at the macroscopic scale, of supersolidity that reconciles (NCRI) and the heat-capacity measurements. The parameters of the Ginzburg-Landau free energy are estimated using experimental data, hence a healing length of the order of $100\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ and a critical speed of the order of $0.1\phantom{\rule{0.16em}{0ex}}\mathrm{m}/\mathrm{s}$ are predicted, both results consistent with recent studies by Kubota and co-workers.