Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session G41: Supersolid |
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Sponsoring Units: DCMP Chair: Norbert Mulders, University of Delaware Room: Baltimore Convention Center 344 |
Tuesday, March 14, 2006 8:00AM - 8:12AM |
G41.00001: Bose-Glass to Superfluid Transition in the 3d Boson Hubbard Model: z=d Peter Hitchcock, Erik Sorensen Recent experiments on cold atomic gases in disordered optical lattices (Schulte \textit{et al.} PRL 95, 170411 (2005)) have renewed interest in the bose-glass to superfluid phase transition in the boson Hubbard model. The dynamical critical exponent z is of central importance to understanding this transition, yet its value at $d > 2$ remains unclear. We present a Monte Carlo study of this transition in the three dimensions. Simulations are performed on the classical (3 + 1) dimensional link-current representation using the geometrical worm algorithm. Finite-size scaling analysis (on lattices as large as 16x16x16x512 sites) of the superfluid stiffness and the compressibility is consistent with the value z = 3 for the dynamical critical exponent, in agreement with existing scaling and renormalization group arguments that z = d. We calculate a value of $\nu = 0.66(2)$ for the correlation length exponent, satisfying the relation $\nu \ge 2/d$ as an equality. [Preview Abstract] |
Tuesday, March 14, 2006 8:12AM - 8:24AM |
G41.00002: Superfluid Glass of He-4 Boris Svistunov, Massimo Boninsegni, Nikolay Prokof'ev With a recently developed worm algorithm, we simulate 800 atoms of He-4 at the density corresponding to the zero-$T$ melting point of the hcp crystal. We find that low-$T$ properties of the system--- in our case, at $T=0.2$K---crucially depend on the initial state and cooling protocol. An ideal hcp crystal is a clear-cut insulator. But if we start with a high-$T$ liquid state and quench-cool the sample down to $T=0.2$K, we end up with a new state of matter, 'superglass',---a metastable amorphous solid that features off-diagonal long-range order and superfluidity. [Preview Abstract] |
Tuesday, March 14, 2006 8:24AM - 8:36AM |
G41.00003: Dynamic Structure Function of a Model Supersolid Chi-Deuk Yoo, Alan Dorsey Second sound, which is a fingerprint of superfluid behavior, can be observed in light scattering through the splitting of the central Rayleigh peak of the thermal diffusion mode into an additional Brillouin doublet of the second sound [1,2]. Since a supersolid undergoes a similar transition as a superfluid, we expect that the Rayleigh peak due to the defect diffusion mode in a normal solid will split into a Brillouin doublet of propagating modes in the supersolid phase. In this work, we have derived the hydrodynamic equations of motion including defects, and obtained both the second sound mode and the dynamic structure function for an isotropic and isothermal supersolid. We find the splitting occurs not only in the transition from a normal fluid to a superfluid but also from a normal solid to a supersolid, which might be observable in light scattering.\newline \newline [1] G. Winterling, F. S. Holmes, and T. J. Greytak, Phys. Rev. Lett. {\bf 30}, 427 (1973). \newline [2] J. A. Tarvin, F. Vidal, and T. J. Greytak, Phys. Rev. B {\bf 15}, 4193 (1977). [Preview Abstract] |
Tuesday, March 14, 2006 8:36AM - 8:48AM |
G41.00004: Landau Theory for the Normal Solid-Supersolid Transition Alan Dorsey, Paul Goldbart, John Toner Kim and Chan [1,2] have reported an anomalous decoupling transition of solid $^4$He in a torsional oscillator measurement, and interpret their results as evidence for non-classical rotational inertia and a possible supersolid phase of $^4$He. Motivated by these results, we [3] have developed a phenomenological Landau theory of the normal-solid to supersolid (NS-SS) transition in which superfluidity is coupled to the elasticity of the crystalline $^4$He lattice. We find that the elasticity does not affect the universal properties of the superfluid transition, so that in an unstressed crystal the well-known $\lambda$-anomaly in the heat capacity of the superfluid transition should also appear at the NS-SS transition. We also find that the onset of supersolidity leads to anomalies in the elastic constants near the transition, that should be observable in sound speed measurements; conversely, inhomogeneous strains in the lattice can induce local variations of the superfluid transition temperature, leading to a broadened transition. \newline \newline [1] E. Kim and M. H. W. Chan, Nature (London) \textbf{427}, 225 (2004). \newline [2] E. Kim and M. H. W. Chan, Science \textbf{305}, 1941 (2004). \newline [3] A. T. Dorsey, P. M. Goldbart, and J. Toner, cond-mat/0508271. [Preview Abstract] |
Tuesday, March 14, 2006 8:48AM - 9:00AM |
G41.00005: Effect of Quantum Correlations on the Vibrational Spectrum of Bosonic Quantum Solids Jorge Sofo We study the effects of quantum correlations on the vibrational spectrum of solids. In particular, we are interested on the description of delocalized zero point vacancies and systems of light atoms interacting through weak dispersion forces, like Helium. We write the interaction Hamiltonian in a basis set of localized oscillators. A decoupling similar to the Random Phase Approximation of the equations of motion exhibits the dependence on particle correlations of the dispersion relation for phonons and consequently the sound speed. The approximation recovers the normal phonon modes in the case of a system described by an uncorrelated wave function. We show that the onset of correlations, as the temperature is lowered, changes the speed of sound, and the vibrational response of the solid. Implications for recent experimental observations of the supersolid state are discussed. [Preview Abstract] |
Tuesday, March 14, 2006 9:00AM - 9:12AM |
G41.00006: Exploration of Vacancies in Solid $4^$He Bryan Clark, David Ceperley Experiments by Kim and Chan [1] have renewed interest in the understanding of supersolids and whether mechanisms exist in solid $^4He$ to allow for supersolid-like effects. Ground state vacancies would lead to bose condensation and superfluidity. Using Path Integral Monte Carlo we examine vacancy formation energies, vacancy-vacancy interactions and the effect of vacancies on supersolid behavior in solid $^4He$. \newline \newline [1] E. Kim and M. H. Chan, Science {\bf 305}, 1941 (2004). [Preview Abstract] |
Tuesday, March 14, 2006 9:12AM - 9:24AM |
G41.00007: Observation of Nonclassical Rotational Inertia in Bulk Solid $^4$He Confined to a Cylindrical Cavity Keiya Shirahama, Motoshi Kondo, Shunichi Takada, Yoshiyuki Shibayama Recent observation of nonclassical rotational inertia (NCRI) in solid $^4$He by Kim and Chan has attracted great interest in physics of supersolid, and motivated a number of theoretical studies. However, there have been surprisingly few experiments to pursuit the nature of their observation. Thus, we have begun a torsional oscillator experiment for bulk solid $^4$He. In order to study the effects of sample geometry and crystal quality, we employ a cylindrical cell, 8 mm high and 8 mm in diameter, which is mounted on an aluminum alloy torsion rod. The resonant torsion frequency is about 1750 Hz, which is $2 \sim 5$ times the frequencies in the Kim and Chan's experiments. In a preliminary experiment we have observed an increase in the frequency below about 250 mK, indicating the existence of NCRI. The frequency shift shows a substantial driving amplitude dependence, which is also consistent with the previous observation. [Preview Abstract] |
Tuesday, March 14, 2006 9:24AM - 9:36AM |
G41.00008: Effect of $^{3}$He impurity on the supersolid transition of $^{4}$He Eunseong Kim, Moses H. W. Chan The supersolid phase of $^{4}$He was revealed by a series of torsional oscillator experiments.[1] One of the most intriguing features of the supersolid transition is the broadening of the transition and the enhancement of T$_{c}$ by the addition of extremely small amount of $^{3}$He impurity. This effect is very different from that in superfluid film and that in `bulk' superfluid helium. We have investigated the$^{ }$influence of $^{3}$He on the supersolid transition by systematically diluting isotopically-pure $^{4}$He ($^{3}$He impurity less than 0.3ppb) with $^{3}$He. [1] E. Kim and M. H. W. Chan, \textit{Science} \textbf{305}, 1941 (2004); \textit{Nature} \textbf{425}, 227 (2004); \textit{J. Low Temp. Phys.} \textbf{138}, 859 (2005) [Preview Abstract] |
Tuesday, March 14, 2006 9:36AM - 9:48AM |
G41.00009: Ballistic Phonon Propagation in Solid $^4$He at Low Temperature Yuki Aoki, Harry Kojima Phonon propagations in hcp solid $^4$He are being studied down to 30 mK including the recently discovered supersolid phase range. Phonons are generated with 2 $\mu$s long heat pulses by applying current into a metal film resistor (of area 5.2 mm$^2$) deposited onto a planar silicon substrate. The power applied to the heater is varied between 20 and 200 $\mu$W/mm$^2$. The phonons travel through 4.3 mm of solid $^4$He and are detected by superconducting edge sensor of 60 nm thick titanium film. In agreement with earlier studies, the main propagation peak detected by the sensor is the transverse sound propagation. Crossover from second sound in normal solid to ballistic propagation is observed between 100 mK and 300 mK at 25 bars. Measurements of ballistic phonon propagation are extended up to 50 bars for the first time. The velocity of transverse phonon propagation increases from 220 m/s at 25 bars to 250 m/s at 50 bars. It is expected that supersolid transition modifies the velocity of transverse sound propagation. It is found, within $\pm$1.5 \% scatter of data, the ballistic phonon propagation velocity(measured at 200 $\mu$W/mm$^2$) remains constant below 100 mK at both 25 and 50 bars. At 30 mK, the velocity is independent of heater power within $\pm$1 \%. [Preview Abstract] |
Tuesday, March 14, 2006 9:48AM - 10:00AM |
G41.00010: Specific heat of solid helium Xi Lin, Anthony Clark, Eunseong Kim, Moses Chan Recently superflow in solid $^{4}$He was found below 200mK via a torsional oscillator technique$^{1}$. While there were a number of measurements on the specific heat of solid helium carried out down to 100mK, there is no evidence of a heat capacity signature related to the onset of the supersolid phase$^{2}$. A serious experimental challenge is discerning the small specific heat of solid helium from that of the metallic cells which are typically used to confine the solid. We have recently begun a new measurement of the heat capacity of solid helium contained in a silicon cell. The heat capacity of the silicon cell below 300mK is always less than that of the solid helium sample. Results of the measurement will be presented. This work is supported by NSF under grant number 0207071. [1] E. Kim and M. H. W. Chan, \textit{Nature} \textbf{427}, 225 (2004); E. Kim and M. H. W. Chan, \textit{Science} \textbf{305}, 1941 (2004); E. Kim and M. H. W. Chan, \textit{J. Low Temp. Phys}. \textbf{138}, 859 (2005). [2] S. H. Castles and E. D. Adams, \textit{J. Low Temp. Phys.} \textbf{19}, 397 (1975); B. H\'{e}bral \textit{et al}., \textit{Phonons in Condensed Matter}, edited by H. J. Maris (Plenum, New York, 1980), pg. 169; A. C. Clark and M. H. W. Chan, \textit{J. Low Temp. Phys}. \textbf{138}, 853 (2005). [Preview Abstract] |
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