Origin of the decrease in the torsional-oscillator period of solid 4He

A decrease in the rotational period observed in torsional oscillator measurements was recently taken as a possible indication of a putative supersolid state of helium. We reexamine this interpretation and note that the decrease in the rotation period is also consistent with a solidification of a small liquidlike component into a low-temperature glass. Such a solidification may occur by a low-temperature quench of topological defects (e.g., grain boundaries or dislocations) which we examined in an earlier work. The low-temperature glass can account for not only a monotonic decrease in the rotation period as the temperature is lowered but also explains the peak in the dissipation occurring near the transition point. Unlike the nonclassical rotational inertia scenario, which depends on the supersolid fraction, the dependence of the rotational period on external parameters, e.g., the oscillator velocity, provides an alternate interpretation of the oscillator experiments.