Figure 1

Experimental configurations. The insets depict I: configuration in Ref. 3, II: details of heat switch, and III: annular channel in the cell. (a) is the mixing chamber; (b), thermal platform; (c), ${}^3\mathrm{He}$ heat switch; (d), ${}^3\mathrm{He}$ fill line; (e), silver sinter heat sink; (f), wound capillary heat sink; (g), ${}^4\mathrm{He}$ fill line; (h), thermal platform; (i), vibration isolator; (j), thermal platform; (k), torsional oscillator base; (l), torsion rod; (m), torsion cell; (n), two electrodes; (o), copper wires; (p), cold finger.Reuse & Permissions

Figure 2

NCRIF (closed symbols) and dissipation (in $Q^{-1}$, open symbols) as a function of temperature for three samples at $P=30$, 53.6, and 136.9 bar. The increases of the resonant period due to the filling of the cell are 2814, 3045, and 3700 ns, respectively. NCRIF measured at the limit of low oscillation speed corresponds to ${\rho }_s/\rho$.Reuse & Permissions

Figure 3

Oscillation speed dependence of normalized NCRIF for five solid helium samples of $P=28.1$, 30, 53.6, 108.3, and 136.9 bar. $v_{\max }$ is the maximum speed of the annulus holding solid ${}^4\mathrm{He}$. NCRIF is normalized by the low temperature supersolid fraction, ${\rho }_{\mathrm{so}}/\rho$. ${\rho }_{\mathrm{so}}/\rho$ for each sample are 0.006 91, 0.006 79, 0.015 44, 0.006 12, and 0.005 76, respectively.Reuse & Permissions

Figure 4

Supersolid fraction in the low temperature limit, ${\rho }_{\mathrm{so}}/\rho$, as a function of pressure. Solid samples prepared with heat switch (new configuration) yield data with less scatter. The solid line is a guide to the eyes.Reuse & Permissions