Evidence for a High-Temperature Disorder-Induced Mobility in Solid $^{4}\mathrm{He}$

Evidence for a High-Temperature Disorder-Induced Mobility in Solid ${}^{4}{He}$

A. Eyal, O. Pelleg, L. Embon, and E. Polturak

Phys. Rev. Lett. 105, 025301 – Published 7 July 2010

Abstract

We have carried out torsional oscillator experiments on solid ${}^{4}{He}$ at temperatures between 1.3 K and 1.9 K. We discovered phenomena similar to those observed at temperatures below 0.2 K, which currently are under debate regarding their interpretation in terms of supersolidity. These phenomena include a partial decoupling of the solid helium mass from the oscillator, a change of the dissipation, and a velocity dependence of the decoupled mass. These were all observed both in the bcc and hcp phases of solid ${}^{4}{He}$ . The onset of this behavior is coincidental with the creation of crystalline disorder but does not depend strongly on the crystalline symmetry or on the temperature.

Received 16 March 2010

DOI:https://doi.org/10.1103/PhysRevLett.105.025301

Authors & Affiliations

A. Eyal^1,*, O. Pelleg², L. Embon¹, and E. Polturak¹

¹Department of Physics, Technion—Israel Institute of Technology, Haifa 32000, Israel
²Brookhaven National Laboratory, Condensed Matter and Materials Science, Upton, New York 11973-5000

^*satanan@tx.technion.ac.il

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Vol. 105, Iss. 2 — 9 July 2010

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Figure 1
Neutron diffraction scans of a bcc ${}^{4}{He}$ crystal. A single crystal produces a sharp and intense diffraction peak (blue circles). The red squares show the effect of stress resulting in a breakup of the single crystal into slightly misoriented grains [19]. We note that this neutron scattering data was obtained in an independent experiment.Reuse & Permissions
Figure 2
Final stages of crystal growth. Time is measured from the beginning of the growth. Small quantities of He are periodically added, momentarily increasing the pressure inside the cell (red symbols) by 130 mbar over the melting pressure ( $28.13 \pm 0.01 bar$ ). As He solidifies in the cell the overpressure decays to zero and the period, $P$ , of the oscillator increases (black symbols). A small pressure step applied to a filled cell at $t = 36.2$ hours compresses the solid enough to disorder the crystal. As a result, $P$ decreases, equivalent to a mass decoupling of 19%. The inset shows $Q^{- 1}$ of the oscillator, which increases upon disordering the crystal. $P$ of an empty cell is $2936.76 μ \sec$ .Reuse & Permissions
Figure 3
Temperature dependence of the decoupled mass fraction (black circles) and of the dissipation $Q^{- 1}$ (green triangles) for an hcp crystal grown from the normal fluid at 1.81 K. Initially, as the crystal is disordered, about 21% of the mass decouples and the $Q$ of oscillations decreases. Upon cooling, both the $Q$ of oscillation and the amount of decoupled mass increase. The inset shows the pressure inside the cell. The solid line in the inset is the melting curve [21]. The open triangles show the temperature dependence of the dissipation of an empty cell.Reuse & Permissions
Figure 4
(a) Temperature dependence of the decoupled mass of a He crystal grown and disordered at 1.64 K. Initially the crystal is bcc. During cooldown the crystal gradually converts to an hcp one. The inset shows the dissipation ( $Q^{- 1}$ ) of the oscillator while cooling. (b) Temperature dependence of the pressure inside the cell during the cooldown (red symbols). The solid line shows the phase diagram [21]. Note that once the crystal reaches the lower triple point (1.464 K), liquid appears in the cell, the decoupled mass fraction vanishes and $Q^{- 1}$ decreases.Reuse & Permissions
Figure 5
Velocity dependence of the mass decoupling. For convenience, all the data sets were shifted to have a common origin. Blue inverted triangles: disordered bcc crystal with 13.6% decoupled mass fraction (at small velocities). For comparison, we show data for: empty cell (black squares); a cell filled with liquid (red circles); and a cell filled with a single crystal (green triangles). The solid line is a fit to an exponential function.Reuse & Permissions

Physical Review Letters

Evidence for a High-Temperature Disorder-Induced Mobility in Solid He4

A. Eyal, O. Pelleg, L. Embon, and E. Polturak

Phys. Rev. Lett. 105, 025301 – Published 7 July 2010

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Evidence for a High-Temperature Disorder-Induced Mobility in Solid ${}^{4}{He}$