Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session A5: Supersolid 4He: A New State of Matter |
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Sponsoring Units: DCMP Chair: John Beamish, University of Alberta Room: Morial Convention Center RO1 |
Monday, March 10, 2008 8:00AM - 8:36AM |
A5.00001: Probable heat capacity signature of the supersolid transition Invited Speaker: We report our heat capacity measurements [1] of solid $^{4}$He down to 40mK, well into the apparent supersolid region of the phase diagram. We observed a broad peak in the specific heat centered near 75mK in $^{4}$He samples containing 1ppb, 0.3ppm, and 10ppm $^{3}$He impurities. In addition, our measurements of samples containing 10ppm and 30ppm of $^{3}$He have revealed a temperature-independent contribution to the heat capacity that scales with the number of isotopic impurities. New measurements with higher resolution are in progress. \newline [1] Nature (London) 449, 1025 (2007). [Preview Abstract] |
Monday, March 10, 2008 8:36AM - 9:12AM |
A5.00002: Probing the upper limit of the nonclassical rotational inertia Invited Speaker: Recently, we have used torsional oscillators to study the dependence of the nonclassical rotational inertia on sample confinement, expressed as surface to volume ratio S/V [1]. When we decreased the width of annular helium sample we observed an increase of the supersolid fraction by three orders of magnitude to 20 \% in a 150 $\mu$m wide annulus. As an extension of those measurements, we have built torsional oscillators with even smaller gaps down to 25 microns. We will give a brief description of the experimental setup and present the results of those measurements. \newline [1] A.S.C. Rittner and J.D. Reppy, Phys. Rev. Lett. \textbf{98}, 175302(2007) [Preview Abstract] |
Monday, March 10, 2008 9:12AM - 9:48AM |
A5.00003: Frequency dependence and Hysteretic behavior in Non-Classical Rotational Inertia of Solid $^{4}$He Invited Speaker: We have constructed a compound torsional oscillator having two resonance frequencies for studying non-classical rotational inertia (NCRI) of solid $^{4}$He. The oscillator allows us to study NCRI and supersolid effects of the \textit{identical} solid $^{4}$He sample grown in a cylindrical container at 496 and 1173 Hz. We have grown and studied solid samples with final solid pressures between 27 and 42 bar. The observed features are qualitatively similar in all solid samples\textbf{.} NCRI fractions at sufficiently low oscillation drive and at the lowest temperature are only about 0.1 {\%} and consistent with cylindrical cells in other laboratories. NCRI fraction below 35 mK does not depend on frequency nor temperature. At T $>$ 35 mK, NCRI fraction observed in the lower mode is smaller than that in the higher mode. ``Transition'' into supersolid state occurs at a higher temperature in the higher mode than the lower one. The peak in extra dissipation due to solid $^{4}$He is greater in the lower mode by a factor 1.7 than in the higher mode. The frequency dependence of the magnitude of NCRI will be compared with existing theoretical predictions. In addition to the frequency dependent effects at low oscillation drive, we have observed hysteretic behavior in NCRI fraction depending on the history of oscillation drive and temperature from the normal state above 300 mK to low temperatures. We find that the supersolid state below 40 mK can have different NCRI fractions depending on the particular sequence of oscillation amplitude. Above about 50 mK, however, NCRI fraction does not depend on the history of oscillation amplitude changes. We also observe a time dependent overshoot in the dissipation of solid when the NCRI fraction is increased by decreasing the oscillation drive. The general behavior of this relaxation phenomenon is rather complex depending on temperature, history of oscillation amplitude and memory effects. Some of the observations share common features with vortex motion and glassy behavior. [Preview Abstract] |
Monday, March 10, 2008 9:48AM - 10:24AM |
A5.00004: Superfluid defects in solid Helium-4: grain boundaries, dislocations, superglass Invited Speaker: First principle quantum Monte Carlo simulations and recent experiments all point out that ideal, defect free, crystals of Helium-4 are not supersolid. Contrary to naive expectation that disorder inhibits superfluidity and suppresses superfluid response due to localization effects, disorder in quantum solids works in the opposite direction: if particles in the ideal crystal are already localized then defects can help to make the sample superfluid. The theory of superfluidity in lower dimensional defective structures embedded in a higher dimensional bulk has its own twists since such phenomena as superfluidity, roughening and defect mobility may be strongly linked. An unusual behavior is expected in the 3D network of 1D liquid channels when normal state at temperatures orders of magnitude above $T_c$ is indistinguishable from that of a superfluid. The possibilities for ``designing'' crystallographic defects are countless, and in the strongly correlated system each case (superfluid or not) has to be considered separately. We find that generic grain boundaries and the screw dislocation along the z-axis are superfluid, while special types of boundaries and edge dislocations are insulating [1,2]. We also find that Helium-4 can form a metastable superfluid glass [3]. Whether these findings are relevant for the explanation of supersolid and other experiments remains an open question. \begin{enumerate} \item L. Pollet, M. Boninsegni, A.B. Kuklov, N.V. Prokof'ev, B.V. Svistunov, and M. Troyer, Phys. Rev. Lett. {\bf 98}, 135301 (2007). \item M. Boninsegni, A.B. Kuklov, L. Pollet, N.V. Prokof'ev, B.V. Svistunov, and M. Troyer, Phys. Rev. Lett. {\bf 99}, 035301 (2007). \item M. Boninsegni, N. Prokof'ev, and B. Svistunov, Phys. Rev. Lett. {\bf 96}, 105301 (2006). \end{enumerate} [Preview Abstract] |
Monday, March 10, 2008 10:24AM - 11:00AM |
A5.00005: Vortex liquid Invited Speaker: |
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