Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session V16: Solid Helium: Experiment |
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Sponsoring Units: DCMP Chair: Haruo Kojima, Rutgers University Room: 317 |
Thursday, March 19, 2009 8:00AM - 8:12AM |
V16.00001: Bose-Einstein condensation in solid helium Richard Azuah, Souleymane Diallo, Oleg Kirichek, Jon Taylor, Henry Glyde We report new measurements of the Bose-Einstein condensate fraction in solid helium. The goal is to reveal whether there is BEC associated with the superfluid fractions that have been observed in solid helium [1,2]. The condensate fraction, n$_0$, is obtained from neutron scattering measurements of the momentum distribution, n(k), of the atoms in the solid. We use commercial grade helium ($^3$He concentration of 0.3 $\%$) where the T$_c$ for superflow is T$_c$ = 200 mK and have measured the n(k) at 3 temperatures, 500 mK, 150 mK and 65 mK. We use a sample cell that has a large surface to volume ratio (S/V) = 40 cm$^{-1}$ where large superfluid fractions have recently been reported[2]. We use a large sample volume (100 cm$^3$) and high instrument resolution to improve precision beyond that of previous measurements [3]. No clear sign of BEC has been observed but the data is being analyzed so that specific values of n$_0$ can be reported. [1] E. Kim and M.H.W. Chan. Science, 305:1941 (2004); Nature, 427:225, 2004. [2]A. S. C. Rittner, and J. D. Reppy, Phys. Rev. Lett., 98:175302, 2007. [3] Diallo et al. Phys. Rev Lett. 98, 205301 (2007). [Preview Abstract] |
Thursday, March 19, 2009 8:12AM - 8:24AM |
V16.00002: Pressure-driven mass flow in solid 4He Ann Sophie C. Rittner, Wonsuk Choi, John D. Reppy We report on two experiments that explore pressure-driven flow in solid 4He. In the first experiment, two pancake-shaped chambers are connected by a narrow slit. The pressure in one chamber is varied periodically at 2 mHz and we look for a superfluid pressure response in the second chamber. When the cell is filled with liquid, we observe a large pressure signal in the second chamber as expected for superfluid flow. In solid helium, no pressure response is detected outside the noise level. In a second experiment, we generate an oscillating pressure in a torsional oscillator by blocking an annulus. We expect the pressure difference to drive the supersolid component through a radial channel orthogonal to the rotational motion of the oscillator. [Preview Abstract] |
Thursday, March 19, 2009 8:24AM - 8:36AM |
V16.00003: Observation of Mass Flux through solid $^4$He Robert Hallock, Michael Ray We have developed a novel apparatus and technique that allows us to maintain an interface between superfluid helium and hcp solid $^4$He at pressures greater than $\approx$ 25 bar, the low temperature solid-liquid coexistence pressure. We use this apparatus to inject helium into one side of the solid, creating a chemical potential difference across the solid, and we then look for a response in the pressure on the other side. We observe a flux of atoms through the solid[1] which tends to decrease with increasing solid pressure. There is also a complicated temperature dependence, which suggests hysteretic behavior. We will describe the experimental apparatus, and some of our results. \\ \\ $[1]$ M.W. Ray and R.B. Hallock Phys. Rev. Lett. \textbf{100} 235301 (2008) [Preview Abstract] |
Thursday, March 19, 2009 8:36AM - 8:48AM |
V16.00004: Growth of hcp Solid $^4$He from the Superfluid Michael Ray, Robert Hallock Using the same experimental apparatus that we developed to search for mass flux in hcp solid $^4$He at pressures greater than 25 bar[1], we study the growth of solid helium from the superfluid at constant temperature. As the pressure of the solid is driven above the melting curve, with helium continuously being added to the sample cell, we observe apparently random events during which the pressure of the solid drops. These pressure drops are accompanied by a sharp transient rise in the temperature of the cell. We will present the data, along with some discussion of what might cause these transients. \\ \\ $[1]$ M.W. Ray and R.B. Hallock Phys. Rev. Lett. \textbf{100} 235301 (2008) [Preview Abstract] |
Thursday, March 19, 2009 8:48AM - 9:00AM |
V16.00005: Velocity dependence of supersolid He-4 in a torsion oscillator. Ethan Pratt, Benjamin Hunt, Vikram Gadagkar, Minoru Yamashita, J.C. Seamus Davis We have developed a free-inertial-decay mapping technique which allows us to acquire the complete velocity-temperature “phase diagram” of supersolid He-4. A striking new feature of the resulting supersolid response map is the appearance of an enhanced dissipation superpeak. We discuss these results in context of various microscopic mechanisms for the velocity-induced suppression of the supersolid response, including a superfluid critical velocity, defect network critical shear, and a glassy dynamical susceptibility. [Preview Abstract] |
Thursday, March 19, 2009 9:00AM - 9:12AM |
V16.00006: Torsional oscillator measurements on solid helium in a partially blocked annular channel Duk Young Kim, Sang-Il Kwon, Hyoungsoon Choi, Eunseong Kim We employed a torsional oscillator technique to investigate the non-classical response of solid helium. We grow solid helium samples within an annular channel that is divided by two Vycor blocks. The melting pressure of helium in narrow pores of Vycor glass is elevated up to about 37 bar due to the strong confinement. This effect is used to engineer various combinations of adjacent helium states. When a helium sample is prepared in the pressure range of 25 and 37 bar a solid-liquid-solid sandwich is formed in and outside the Vycor. Non-classical rotational inertia fraction (NCRIF) of 0.02{\%} is observed under this circumstance below about 200mK. For the pressure higher than 37 bar Vycor glasses in the channel can be utilized as partial blocks and the strength of blockage can be modified by gas adsorption on to the pore wall. Supersolid behavior with a number of different partial blockages will be presented. [Preview Abstract] |
Thursday, March 19, 2009 9:12AM - 9:24AM |
V16.00007: Simultaneous Oscillation of Annular Solid $^4$He Samples at Two Mode Frequencies in Compound Torsion Pendulum Michael C. Keiderling, Harry Kojima We have extended our studies on the non-classical behavior of solid $^4$He contained in compound torsional oscillator (TO) cell below 1 K. Our unique TO design allows observations on the identical sample at two distinct frequencies(f$_1$=493 and f$_2$=1165 Hz). The sample was grown by blocked capillary method in an annular cell(id = 8.0 mm, od = 10.0 mm, height = 9.0 mm). We focus here on experiments in which the two modes are excited simultaneously. While keeping the drive of f$_2$ mode at a very low level, the drive of f$_1$ mode was varied from high to low levels to produce substantial variations in the non-classical rotation inertia fraction (NCRIf). When the NCRIf seen by f$_1$ mode is reduced by 89, 91 and 94 \% at 9.7, 23.5 and 56.5 mK, respectively, the NCRIf seen by f$_2$ mode (driven at low level) is reduced by 62, 68 and 80 \%. The discrepancies and their temperature dependence in the observed reductions in NCRIf are not yet understood. Similar Measurements with the roles of the drive levels of the modes reversed as well as the changes in the dissipation of the torsional oscillator during the simultaneous drive will be reported. [Preview Abstract] |
Thursday, March 19, 2009 9:24AM - 9:36AM |
V16.00008: Effects of $^3$He Impurities on the Non-Classical Rotation Inertia of Solid $^4$He as Measured by Compound Torsion Pendulum David Ruffner, Michael Keiderling, Patryk Gumann, Harry Kojima An intriguing observation related to the discovery of non-classical rotational inertia(NCRI) of solid $^4$He at low temperatures is the extreme sensitivity to $^3$He concentration(x$_3$). Both the magnitude and temperature dependence of the NCRI are affected by relatively low x3 introduced into solid $^4$He samples.[1] We are exploring the $^3$He impurity effect using our compound torsional pendulum which allows probing the NCRI of the identical solid $^4$He sample at two different frequencies ($\sim$493 and $\sim$1165 Hz). The NCRI fractions were derived from the measured shifts in the oscillator frequency of the two modes as functions of temperature. The NCRI fraction derived from the higher frequency mode is greater than that derived from the lower frequency mode at all temperatures. If the NCRI fractions of both modes are normalized at their maximums, the temperatures at which they decrease to 50 \% of the maximum are greater in the higher mode by $\sim$9, 31 and 56 mK when the nominal x$_3$ added is 0.3, 3 and 10 ppm, respectively. Greater values of x$_3$ are currently being studied.[1]Kim, et al., Phys. Rev. Lett. \textbf{100} 065301(2008). [Preview Abstract] |
Thursday, March 19, 2009 9:36AM - 9:48AM |
V16.00009: Sample quality dependence of the specific heat peak in solid $^{4}$He Xi Lin, Z. G. Cheng, M. H. W. Chan We reported a broad peak in specific heat of solid $^{4}$He[1] at a temperature near the onset of Non-Classical Rotational Inertia (NCRI). This peak is likely to be a thermodynamic signature of the supersolid phase. Since it was found that the supersolid fraction is dependent upon the sample quality[2,3], we are motivated to study the sample quality influence on solid $^{4}$He specific heat. In our recent measurements, we have confirmed the presence of a broad peak in the specific heat of solid $^{4}$He below $\sim $200mK in addition to the phonon contribution. We also show how the excess specific heat peak changes with sample quality. 1 X. Lin, A. C. Clark, and M. H. W. Chan, Nature 449, 1025 (2007). 2 A. S. C. Rittner and J. D. Reppy, Phys. Rev. Lett. 98, 175302 (2007). 3 A. C. Clark, J. T. West and M. H. W. Chan, Phys. Rev. Lett. 99, 135302 (2007). [Preview Abstract] |
Thursday, March 19, 2009 9:48AM - 10:00AM |
V16.00010: Torsional oscillator and specific heat studies of 4He in Vycor Z.G. Cheng, X. Lin, J.T. West, M.H.W. Chan Non-classical rotational inertia (NCRI) was first reported in solid helium confined in Vycor using the torsional oscillator technique [1]. Most of the work since then has focused on bulk solid helium. Recent specific heat measurements of bulk solid helium show a peak centering near the NCRI onset temperature [2], a good indication that the two may be related. We report on a series of experiments to study the NCRI fraction and specific heat of solid helium in Vycor. The torsional oscillator experiment is revisited to study the stability of the NCRI fraction. The purpose of the specific heat measurement is to probe the relation between the specific heat peak and NCRI. \\[3pt] [1] E. Kim, M. H. W. Chan, Nature 427, 225 (2004). \\[0pt] [2] X. Lin, A. C. Clark, M. H. W. Chan, Nature 449, 1025 (2007). [Preview Abstract] |
Thursday, March 19, 2009 10:00AM - 10:12AM |
V16.00011: Second sound in supersolid $^{4}$He Norbert Mulders, Sangil Kwon, Eungseong Kim In a system that consists of two interpenetrating continuous phases that are free to move with respect to each other, one would expect to find two longitudinal sound modes. A good example is fourth sound in superfluid helium in a porous matrix, but the phenomena can also be observed with water in rocks. If one interprets the observation of a non-zero NCRIF in solid helium below $\sim $100 mK as due to the independent motion of a supersolid fraction with respect to the crystal, it follows that two longitudinal sound modes should exist, with the slow mode disappearing at the supersolid transition. We will report on our efforts to find this slow mode. [Preview Abstract] |
Thursday, March 19, 2009 10:12AM - 10:24AM |
V16.00012: Supersolidity of Solid $^4$He Confined in 25 Angstrom Nanopores Keiya Shirahama, Hitomi Yoshimura, Yoshiyuki Shibayama There has been growing consensus that dislocations play an important role on the supersolid behaviors observed in torsional oscillator experiments for solid $^4$He. When solid He is confined in nanopores, dislocations may not exist, or even if they exist their motion is suppressed, and supersolidity should therefore be greatly modified. Study of solid 4He in confined geometries may therefore give an important clue to elucidate the mechanism of supersolidity. Earlier studies of solid 4He in Vycor by Kim and Chan [1] found no difference in the supersolid behaviors from bulk solid. We have performed torsional oscillator experiments for solid $4$He in a porous Gelsil glass that has nanopores of 25 angstroms in diameter. We have observed an increase in oscillator frequency indicating supersolidity below 200 mK. This result suggests that the existence of dislocations is not a necessary condition for supersolidity. [1] E. Kim, M. H. W. Chan, Nature 427, (2004) 225. [Preview Abstract] |
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