Observation of Classical Rotational Inertia and Nonclassical Supersolid Signals in SolidHe4below 250 mK

Abstract

We have confirmed the existence, as first reported by Kim and Chan, of a supersolid state in solid 4 He at temperatures below 250 mK. We have employed a torsional oscillator cell with a square cross section to insure a locking of the solid to the oscillating cell. We find that NCRI signal is not a universal property of solid 4 He, but can be eliminated through an annealing of the solid helium sample. This result has important implications for our understanding of the supersolid state. He confined within the porous media of porous gold and Vycor glass. KC followed this remarkable discovery with the observation of a supersolid or non-classical rotational inertia (NCRI) signal in bulk solid helium [2]. An important goal, which we have achieved in our experiments, has been to provide an independent confirmation of the KC observations for bulk 4 He. We have also investigated the influence of annealing and sample preparation on the existence of the supersolid state. We find that the supersolid state is not a universal property of solid 4 He, but that it is possible through crystal annealing near the melting curve to create samples that show only classical rotational inertia (CRI).In these measurements we have employed the torsional oscillator technique developed at Cornell over the past several decades [4]. Oscillators with two different sample geometries were used in the experiments reported in this letter. The first had a cylindrical sample geometry with an internal volume of 2.7 cm 3 and operated at a frequency of 253 Hz, while the second had a cubic geometry with a volume of 1.4 cm 3 and operated at 185 Hz. The helium used in the experiments was commercial well-grade helium similar to that used by KC in their bulk solid helium work [2]. This helium has a stated 3 He impurity level of 0.2 -0.3 ppm.Our earliest runs were made with the cylindrical cell. Data obtained with this cell at a pressure of 27 bar showed an onset of the supersolid signal at a temperature near 0.2 K, with a maximum signal amplitude at 30 mK of 0.6 % of the total period shift seen upon forming the solid in the cell. The magnitude of this signal is in good agreement with the observations of KC made under similar conditions and provides a confirmation of their results. In an attempt to improve the size of our NCRI signal we increased the sample pressure toward 55 bar. The cell failed before reaching this pressure.A diagram of our second cell is shown in Fig. 1. The design is similar to that of our first cell with several significant modifications. First, we have converted the The torsion cell's motion is excited and detected capacitively. The AC voltage on the detection electrodes serves as reference signal for a lock-in amplifier to keep the oscillation in resonance. At 4 K, the mechanical quality factor is 9 x 10 5 , and the resonance frequency is 185 Hz.interior of the cell to a nearly cubic geometry by epoxying a Tellurium-Copper insert into the cylindrical volume of the Beryllium-Copper oscillator. The insert was machined to provide a cubic ...

Quenched Dislocation Enhanced Supersolid Ordering

“…The T clean c < 0 scenario is supported by recent experiments [14], showing non-classical rotational inertia in unannealed 4 He crystals, but none after annealing. On the other hand, Chan's recent experiments [11], as discussed above and in figure (2), suggest T clean c > 0.…”

NMR Study of the Dynamics ofHe3Impurities in the Proposed Supersolid State of SolidHe4

“…The discovery of a non-classical rotational inertia fraction (NCRIF) in solid 4 He by Kim and Chan [1,2] has generated enormous interest because the NCRIF could be the signature of a supersolid state [3]. Several independent experiments [4,5] have shown that the NCRIF magnitude and temperature dependence are strongly dependent on defects such as 3 He impurities and the quality of the crystals. Recently studies of the elastic properties of solid 4 He by Beamish and colleagues [6] have revealed a significant frequency dependent change in the elastic shear modulus with an enhanced dissipation peak having a temperature dependence comparable to that observed for the NCRIF.…”

Disorder and the Supersolid State of SolidHe4

“…Following the discovery by Kim and Chan (KC) [1, 2] of the supersolid or nonclassical rotational inertia (NCRI) state of bulk solid 4 He, several independent groups using the same torsional oscillator technique have confirmed the KC supersolid results. These include the Japanese groups of Shirahama et al [3], working at Keio University, and Kubota et al [4] at the ISSP, as well as our group [5] at Cornell University. In these early experiments, the solid samples were formed by the blocked capillary technique.…”

“…These include the Japanese groups of Shirahama et al [3], working at Keio University, and Kubota et al [4] at the ISSP, as well as our group [5] at Cornell University. In these early experiments, the solid samples were formed by the blocked capillary technique.…”