Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session A41: Quantum Fluids and Solids |
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Sponsoring Units: DCMP Chair: Haruo Kojima, Rutgers University Room: Baltimore Convention Center 344 |
Monday, March 13, 2006 8:00AM - 8:12AM |
A41.00001: Specific heat of liquid He-4 near the superfluid transition and confined in cylindrical channels Tahar Aouaroun, Guenter Ahlers We present new measurements of the specific heat near the lambda transition of liquid He-4 at saturated vapor pressure and confined in micro-channel plates containing cylindrical holes. We investigated two channels diameters: 1$\mu$m and 2$\mu$m. Our results for the scaling function near the specific-heat maximum are in reasonably good agreement with previous measurements on channels with a 1 $\mu$m $\times$ 1 $\mu$m square cross section\footnote{M.O. Kimbal, K.P. Mooney, and F.M. Gasparini, Phys. Rev. Lett. {\bf 92}, 115301 (2004)} and on cylindrical channels with a 0.26$\mu$m diameter\footnote{J.A. Lipa, M. Coleman, and D.A. Stricker, J. Low Temp. Phys. {\bf 124}, 443 (2001)}. They also are consistent with the scaling function derived from Monte Carlo calculations.\footnote{N. Schultka and E. Manousakis, J. Low Temp. Phys. {\bf 111}, 783 (1998)} However, they suggest a size- dependent systematic departure from a unique scaling function that is consistent with earlier measurements$^3$ on cylindrical channels of 8$\mu$m diameter. [Preview Abstract] |
Monday, March 13, 2006 8:12AM - 8:24AM |
A41.00002: Deformation and damage in silica aerogels during fluid filling Tobias Herman, John Beamish Interfaces are present throughout any porous medium during fluid adsorption below the liquid-vapor critical point. Surface tension in these curved liquid-vapor interfaces produces the pressure difference between the two phases which is responsible for capillary condensation. The surface tension also exerts a force on the solid, although it is usually much smaller than the elastic moduli of the porous medium. Aerogels, however, have extremely small elastic moduli so surface tension induced deformation can be significant and even destructive. We present measurements of the dilation and compression of two silica aerogels (densities 110 and 51 kg/m$^3$) during adsorption and desorption of low surface tension fluids (helium and neon). The denser aerogel changed its length by up to 2\% during adsorption of helium, still within its elastic regime; the lighter aerogel shrank by even larger amounts and appeared to sustain permanent damage. [Preview Abstract] |
Monday, March 13, 2006 8:24AM - 8:36AM |
A41.00003: Cryogenic Pulsed Laser Deposition of Lithium for $^{4}$He Absorption Experiments E. Van Cleve, P. Taborek, J.E. Rutledge We are developing techniques to prepare films of alkali metals on cryogenic surfaces by laser ablation. The alkali metals are known to provide weak adsorption potentials for $^{4}$He which results in nontrivial wetting and superfluid onset phenomena. Film preparation technique strongly affects some $^{4}$He wetting properties as has been seen in contact angle measurements of $^{4}$He on Cs surfaces. Of particular interest are Li surfaces which at low temperatures are predicted (1) to be superfluid with less than monolayer total $^{4}$He coverage. We have grown Li films on using 532 nm light from an Nd-YAG laser on to room temperature quartz crystal microbalances (QCM). We will present measurements of film growth rate as a function of the laser fluence. Preliminary $^{4}$He isotherm measurements on Li films laser ablated onto 4K QCMs will be compared with adsorption isotherms on the heavier alkali metal surfaces. $\linebreak$ $\linebreak$ (1) Massimo Boninsegni and Milton W. Cole, J. Low Temp. Phys. 113, 393 (1998). [Preview Abstract] |
Monday, March 13, 2006 8:36AM - 8:48AM |
A41.00004: Acoustic crystallization Sebastien Balibar, Ryosuke Ishiguro, Frederic Caupin By focusing high intensity acoustic waves in the middle of a liquid, it is possible to pressurize it far beyond its solid-liquid equilibrium pressure. This is because, in the absence of walls or defects, the nucleation of crystals needs to be ``homogeneous'', and that the threshold pressure for this phenomenon is usually very high. In a classical liquid, the viscosity increases with pressure so that the dynamics blocks as the pressure is increased and a transition to a glassy state occurs. However, we did not expect this to occur in a superfluid, and we looked for acoustic crystallization in liquid helium. We have found evidence that an acoustic wave travelling in superfluid helium can indeed crystallize this liquid on its path. We relate this phenomenon to the existence of an instability where Landau's ``rotons'' become soft modes. We discuss further developments of this experiment in relation with the existence of superfluidity in a very dense liquid. [Preview Abstract] |
Monday, March 13, 2006 8:48AM - 9:00AM |
A41.00005: Bose-Einstein Condensation and atomic kinetic energies in liquid $^3$He-$^4$He mixtures Souleymane Diallo, Jonathan Pearce, Richard Azuah, Henry Glyde We present neutron scattering measurements of the momentum distribution of liquid ${^3}$He-${^4}$He mixtures. The experiments were performed at wavevectors $Q$, 26 $\leq$ $Q$ $\leq$ 29 \AA$^{-1}$, on the MARI time-of-flight spectrometer at the ISIS pulsed spallation neutron source. Mixtures with $^3$He concentrations $x$ between 0 and 20\% were investigated both in the superfluid and normal phases. From the data, we extract, to new accuracy, the Bose-Einstein condensate fraction $n_0$ and the momentum distributions of $^3$He and $^4$He atoms. We find an increase in $n_0$ above the pure $^4$He value; from 7.25$\pm$0.75\% ($x=0\%$) to 11.2$\pm$1.85\% at $x=15\%$, in agreement with theoretical calculations but in disagreement with the only other measurement. The $^4$He kinetic energy, $\backslash$kef, is found to be largely independent of $x$. The $^3$He momentum distribution $n(\bf{k})$ is not well fitted with a Fermi step function alone. A high momentum tail in $n(\bf{k})$ is needed to get a good fit - a tail that is consistent with calculated tails in $n(\bf{k})$. The $^3$He atomic kinetic energy, $ K_3$, is determined almost entirely by this tail. It is therefore not a well determined single property for comparing theory and experiment. This finding resolves a long-standing discrepancy on $ K_3$ between theory and experiment. [Preview Abstract] |
Monday, March 13, 2006 9:00AM - 9:12AM |
A41.00006: Bose-Einstein Condensation in liquid $^4$He films Jonathan Pearce, Souleymane Diallo, Richard Azuah, Tom Arnold, John Larese, Henry Glyde Neutron scattering measurements of Bose-Einstein condensation in liquid $^4$He fils will be presented. The measurements were carried out on the MARI time-of-flight spectrometer at the CCLRC ISIS Facility, Rutherford Appleton Laboratory, UK. The goal is to determine whether the condensate fraction, $n_0$, is enhanced above the bulk liquid value at a liquid $^4$He surface. It is also to determine $n_0$ in 2D thin films and, by varying the film thickness, observe a 2D to 3D cross-over. Data for films on a flat MgO substrate [1] and on carbon-black will be presented. The data shows, that $n_0$ is indeed significantly enhanced at a film - vapor surface suggesting a lower liquid density there [2]. \newline \newline [1] J.V. Pearce {\em et al.}, {\em J. Phys. Condens. Matter} {\bf 16}, 4391 (2004) \newline [2] E.W. Drager and D.M. Ceperley, {\em Phys. Rev. Lett.} {\bf 89}, 15301 (2002) [Preview Abstract] |
Monday, March 13, 2006 9:12AM - 9:24AM |
A41.00007: Bilayer Thermometers for Third Sound Detection J.D. Cummings, R.B. Hallock We present results from an experiment to develop bilayer metallic films of aluminum and gold as superconducting transition edge thermometers for the detection of third sound waves. Generally, traditional transition edge thermometers operate in a temperature range that is dictated by the choice of superconductor, e.g. $\sim$ 1.5K for aluminum and $\sim$ 0.8K for zinc, which is tunable over a modest range by application of a magnetic field or bias current. Bilayers offer the option of selecting the optimal transition temperature for an experiment to be done by adjusting the ratio of normal metal (Au) thickness to the superconductor (Al) thickness. This allows a detector to be designed to operate at any temperature below the transition temperature for the pure superconducting film. We will present transition edge data for such thermometers and document their utility for third sound detection. [Preview Abstract] |
Monday, March 13, 2006 9:24AM - 9:36AM |
A41.00008: Anomalous Coupling Between Superfluid Vortices and Curvature Ari Turner, Vincenzo Vitelli, David Nelson Vortices in a thin film of superfluid helium on a curved surface are predicted to have a long range interaction with the curvature of the surface. Vortices are trapped by features of the surface with appropriate Gaussian curvature. The energetics will be compared and the dynamics contrasted with those of particles experiencing a two dimensional Coulomb force. [Preview Abstract] |
Monday, March 13, 2006 9:36AM - 9:48AM |
A41.00009: SQUID NMR Studies of Two-Dimensional $^3$He Films on HOPG ZYX Graphite Jinshan Zhang, Lei Guo, Yuliang Du, C.M. Gould, H.M. Bozler SQUID NMR experiments on the second layer of $^3$He films on Grafoil substrates in the low field limit found ferromagnetic ordering for coverages over 20 atoms/nm$^2$. The appearance of ordering in a two-dimensional magnetic film can be caused by weak anisotropy and/or dipolar interactions, or could be a manifestation of finite size effects. By replacing Grafoil with Highly Oriented Pyrolytic Graphite (HOPG) ZYX grade, we increased the substrate structural coherence length by a factor of 10 in order to study the importance of finite size effects through a magnetization measurement on 2-D $^3$He films. Our recent experiments found the ferromagnetic ordering temperature to be the same or higher on ZYX than on Grafoil at coverages over 20 atoms/nm$^2$, showing no evidence for an increased suppression of the ordering due to the increasing coherence length. We also saw evidence for bound spin waves in the ordered layer. Studies in the coverage range 20-24 atoms/nm$^2$ are complicated by the possibility of coexistence of two phases. Recently we extended our measurements to higher coverages where the situation is less complicated and a single incommensurate solid phase is formed unambiguously. We report on these studies which continue to support the picture of a 2-D magnetically ordered solid. *Supported by NSF through grant DMR-0307382 [Preview Abstract] |
Monday, March 13, 2006 9:48AM - 10:00AM |
A41.00010: Ultrasonic Spectroscopy in Liquid $^{3}$He in 98{\%} Porosity Aerogel by Direct Propagation H.C. Choi, N. Masuhara, J.-H. Park, M.W. Meisel , Y. Lee, N. Mulders Systematic investigations on the effect of static disorder on \textit{p-wave} superfluid $^{3}$He have been made possible by utilizing its unique structure of high porosity silica aerogel. For the past 10 years, a burst of experimental effort revealed that three distinct superfluid phases exist in the P-H-T phase diagram of the $^{3}$He/98{\%} aerogel system. These three phases are conveniently named the A-, B-, and A$_{1}$-phases as in the bulk, although only spin structures of the superfluid phases have been identified. In particular, the verdict on the so called A-phase is by no means conclusive. As has been the case in the bulk, for a clear identification of the order parameter structure, both spin and orbital components need to be examined. We report our preliminary results of sound propagation in an attempt to directly investigate the orbital structure of the superfluid phases in 98{\%} aerogel using a pulsed ultrasound spectroscopic technique. Preliminary data for the transmission and the surface impedance will be presented. [Preview Abstract] |
Monday, March 13, 2006 10:00AM - 10:12AM |
A41.00011: Transverse acoustic spectroscopy of Superfluid $^{3}$He in compressed aerogel. P. Bhupathi, H. C. Choi, J. Jhaveri, B. H. Moon, Y. Lee In light of the recent developments on the A-B transition in superfluid $^{3}$He in aerogel and the effect of anisotropic scattering$^{2}$, we have designed an experiment to perform transverse acoustic impedance measurements on compressed aerogel. We investigate the effect of global anisotropy on the phase transition, generated by introducing uniaxial compression of 5 {\%} on the aerogel. We report our preliminary results together with the measurements on the uncompressed aerogel. [Preview Abstract] |
Monday, March 13, 2006 10:12AM - 10:24AM |
A41.00012: Spin Relaxation Phenomenon in Superfluid $^3$He A$_1$ H. Kojima, S. Kobayashi, A. Yamaguchi, H. Ishimoto The spin relaxation phenomenon in superfluid $^3$He A$_1$ phase is studied using a newly constructed magnetic fountain pressure cell in which two reservoirs are connected via a superleak channels of height 20 $\mu$m. Experiments are carried out to explore the relaxation mechanism of the induced fountain pressure under externally applied magnetic field gradient along the superleak. The relaxation of fountain pressure reflects that of spin density. The observed relaxation time $\tau$ varies from less than 1 s near T$_{c2}$ to about 80 s near T$_{c1}$. The maximum relaxation time may be limited by the normal fluid flow in the channels. Near T$_{c2}$, the observed relaxation rate may be described by a power law dependence on reduced temperature as $1/\tau \propto [(T-T_{c2})/(T_{c1}-T_{c2})]^{-\beta}$, where $\beta \approx 1.5$ and has little dependence on the static magnetic field(up to 8 tesla) and liquid pressure(10 - 29 bars). To our knowledge, there is no theory which predicts such increase in relaxation rate over a relatively large temperature range near T$_{c2}$. A preliminary interpretation is given in terms of intrinsic spin relaxation arising from small but increasing presence of minority spin pair condensate in A$_1$ phase as T$_{c2}$ is approached. [Preview Abstract] |
Monday, March 13, 2006 10:24AM - 10:36AM |
A41.00013: Measurements of Longitudinal and Transverse NMR Frequencies in Superfluid $^3$He using dc SQUID Detectors Yuliang Du, H.M. Bozler, C.M. Gould The most important tools in the initial identification of the order parameters of the superfluid phases of $^3$He in bulk were longitudinal and transverse NMR because the detailed comparison of these frequencies and their magnetic field dependences strongly differentiated between alternative models. In contrast, for superfluid $^3$He confined within aerogel, longitudinal resonance has not been measured to date, having only been inferred from transverse measurements and the simple sum of squares relation known to hold for the axial state in bulk. This relationship has not been confirmed for the aerogel-confined phase, and there are theoretical suggestions that it may not be valid. We have begun an experiment to directly compare longitudinal and transverse resonance frequencies in aerogel-confined superfluid $^3$He using some of the same dc SQUID NMR techniques we have developed over the last 20 years in our lab. In initial experiments to prove the technique, we are making optimal use of the broadband nature of the dc SQUID detector and have measured the superfluid's longitudinal response to a sudden field step. [Preview Abstract] |
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