Nonsuperfluid Origin of the Nonclassical Rotational Inertia in a Bulk Sample of Solid ${}^4\mathrm{He}$

The torsional oscillator experiments described here examine the effect of disorder on the nonclassical rotational inertia (NCRI) of a solid ${}^4\mathrm{He}$ sample. The NCRI increases with increasing disorder, but the period changes responsible for this increase occur primarily at higher temperatures. Contrary to expectations based on a supersolid scenario, the oscillator period remains relatively unaffected at the lowest temperatures. This result points to a nonsuperfluid origin for the NCRI.

Figure 1

The torsional oscillator, consisting of three sections, is shown in cross section. The body and torsion rod are made from a single piece of hardened BeCu alloy. The other sections, including the flexible diaphragm, were machined from a high strength aluminum alloy. The Straty-Adams gauge electrodes are brass, and the upper fill line consists of a section of CuNi tubing with an internal diameter of 0.01 cm.

Figure 2

Period data for the initial sample of bulk solid ${}^4\mathrm{He}$ are shown in red as a function of temperature. The period data obtained following the deformation of the sample by an application of 10.3 bar to the flexible diaphragm are plotted in blue. The bottom data, plotted in black, are the period data for the empty cell shifted upward by 110 ns.

Figure 3

Data for the period shift between the period following deformation and the period of the initial sample are plotted as functions of the temperature. The lower data set, in red, was obtained after a pressure of 10.3 bar had been applied to the flexible diaphragm, while the second set with the larger period increase was obtained after the application of 13.8 bar.

Figure 4

Dissipation data for the empty cell are plotted in black, the initial sample in red, and the data for the sample after deformation in blue. Note that the dissipation data for the empty cell have not been shifted. At the lowest temperature all three data sets have the same dissipation.

Figure 5

Period data for a series of temperature sweeps, including high temperature annealing, are shown as a function of temperature.