Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session L33: Quantum Fluids and Solids II |
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Sponsoring Units: DCMP Chair: Rena Zieve, UC Davis Room: LACC 511C |
Tuesday, March 22, 2005 2:30PM - 2:42PM |
L33.00001: Simulation of Helium-4 in Aerogel Marios Nikolaou, Mats Wallin, Hans Weber The superfluid 4He transition in highly porous silica glasses, like aerogel and xerogel, have been studied experimentally [1]. The experiments obtain critical exponents that deviate from the bulk exponents for low porosity of the silica glass, and obtain evidence for violations of hyperscaling. We study this transition as a function of porosity within fractal diluted 3DXY models. We use the Wolff collective update method and go to larger system sizes than in previous simulation studies of the problem. We obtain results for the critical properties of the transition and compare with experiments. \\ 1. J. Yoon et al., Phys. Rev. Lett. 80, 1461 (1998) [Preview Abstract] |
Tuesday, March 22, 2005 2:42PM - 2:54PM |
L33.00002: Finite-size effects on the thermal conductivity of $^4$He confined in rectangular channels. Sergei Jerebets, Yuan-Ming Liu, Feng-Chuan Liu, Guenter Ahlers We report results for the thermal conductivity $\lambda(t)$ of $^4$He confined in glass capillary arrays with rectangular channels of size $1\times10\times1000~\mu{\rm m}^3$ near the bulk super-fluid transition temperature $T_\lambda$ as a function of the reduced temperature $t \equiv T/T_{\lambda} - 1$. Even close to $T_\lambda$ we found that $\lambda(t)$ differs very little from similar measurements for cylindrical channels of radius $1~\mu$m, \footnote{D. Murphy, E. Genio, G. Ahlers, F.C. Liu, and Y. Liu, Phys. Rev. Lett. {\bf 90}, 025301 (2003).} indicating similar scaling functions for the two geometries. This differs from the finite-size effects on thermodynamic properties, which have very different scaling functions near the transition for parallel-plate and cylindrical geometries.\footnote{M. O. Kimball, K. P. Mooney, and F. M. Gasparini, Phys. Rev. Lett. {\bf 92}, 115301 (2004).} [Preview Abstract] |
Tuesday, March 22, 2005 2:54PM - 3:06PM |
L33.00003: Scaling of thermal resistivity of $^4$He in restricted geometries Chongshan Zhang, D. P. Landau The thermal resistivity and its scaling function in quasi-2D $^4 $He systems are studied by Monte Carlo and spin-dynamics simulation of the classical 3D XY model on $L \times L \times H$ lattices with $L \gg H$. Open boundary conditions are applied along the $H$ direction and periodic boundary conditions along the $L$ directions. A hybrid Monte Carlo algorithm is adopted to efficiently deal with the critical slowing down \footnote{M. Krech and D. P. Landau, Phys. Rev. B {\bf 60}, 3375 (1999)}. Fourth-order Suzuki-Trotter decomposition of exponential operators is used to solve numerically the coupled equation of motion for each spin. The thermal conductivity is calculated by a dynamic current- current correlation function. Our results are consistent with a universal scaling function $F (X)=(L/ \xi_0)^{\pi/ \nu} ( \rho / \rho_0)$, $X=(L/ \xi_0)^{1/ \nu}t$ using known values of the critical exponents $\pi$ and $\nu$ $(\rho = \rho_0 t^{- \pi} $ is the thermal resistivity , and $\xi = \xi_0 t^{- \nu}$ is the correlation length). The thermal resistivity scaling function agrees well with the available experimental results \footnote{Experimental data provided by G. Ahlers, S. Jerebers, Y. Liu and F. C. Liu} for slabs using the temperature scale and thermal resistivity scale as free fitting parameters. \\ \\ $^*$Research supported by NASA [Preview Abstract] |
Tuesday, March 22, 2005 3:06PM - 3:18PM |
L33.00004: Continuous-Wave Measurement of the Upward-Going Temperature Wave in the Helium-4 Self-Organized-Critical State Near the Lambda Transition R.V. Duncan, S.T.P. Boyd, D.A. Sergatskov We describe the first continuous-wave (CW) measurements of the upward-going temperature wave in the self-organized-critical (SOC) state which forms in $^4$He under conditions of downward heat flow near $T_{\lambda}$ under gravity. The CW technique permits measurements with extremely low ($<1$ nK) excitation amplitudes, allows continuous measurement of the wave velocity as the SOC state grows, and has yielded the first quantitative measurements of the attenuation. The measured attenuation disagrees with predictions, and this new technique may help address the question of whether the SOC state is occurring in the helium-I or helium-II state. Some intriguing new qualitative features are also described. [Preview Abstract] |
Tuesday, March 22, 2005 3:18PM - 3:30PM |
L33.00005: Temperature Gradient of Hydrodynamic Origin in Vertically Counterflowing Helium-II Near the Lambda Transition Under Gravity S.T.P. Boyd, R.V. Duncan We describe a calculation of the temperature gradient occurring in helium-II near $T_{\lambda}$ when it transports a uniform energy flux density vertically upward or downward under gravity. The calculation is performed within the dissipationless two- fluid model and assumes 1D and steady- state. An exact solution is obtained which indicates a temperature gradient of hydrodynamic origin in which both the gravitational hydrostatic pressure head and the suppression of the superfluid component density $\rho_s$ by the counterflow velocity $w^2=(v_n-v_s)^2$ play essential roles. The temperature gradient is very small for temperatures well below $T_{\lambda}$ and rises toward a limiting value of $dT_ {\lambda}/dz$ as temperature is increased. It is quadratic in the component fluid flow velocities and thus its sign, remarkably, is independent of the sign of the heat flow. The predicted gradient occurs in a narrow temperature range and it is not clear if it will be directly observable. However, its existence may provide some insight into the recently-discovered up-down heat flow asymmetry in the ``thermal resistance'' of helium-II near $T_{\lambda}$. [Preview Abstract] |
Tuesday, March 22, 2005 3:30PM - 3:42PM |
L33.00006: Precise equation of state measurements of $^4$He near the $\lambda$-point, using dual-mode Superconducting Cavity Stabilized Oscillators T.A. Corcovilos, D.M. Strayer, N.N. Asplund, N.-C. Yeh We report on progress towards precise equation of state measurements of $^4$He saturated vapor near the $\lambda$-point using a Superconducting Cavity Stabilized Oscillator (SCSO) system. By operating the SCSO in a dual-mode phase-locked loop configuration we will be able to measure the dielectric constant of $^4$He to parts in $10^{15}$ precision and comparable accuracy. The dielectric constant in turn implies a value of the density to parts in $10^{10}$. Other measured parameters include the temperature to sub-nK precision using paramagnetic salt high-resolution thermometry (HRT) and pressure to parts in $10^9$ using a Straty-Adams type diaphragm gauge. These substantially improved resolutions relative to existing data are expected to provide new insights into the interactions of helium atoms near Bose-Einstein condensation. Numerous error reduction techniques will be discussed, along with other applications of SCSO to precision metrology. [Preview Abstract] |
Tuesday, March 22, 2005 3:42PM - 3:54PM |
L33.00007: 1-D Numerical Simulation of Heat Transfer near the Liquid-Vapor Critical Point Fang Zhong, Martin Barmatz Near a liquid-vapor critical point, a constant volume fluid undergoes both a fast adiabatic and a slow diffusive heat transfer when heated at the boundary. Earlier numerical studies of this equation revealed the main features of the solution. This numerical technique had many limitations, such as large errors for a highly nonlinear system very close to the critical point, or for a fast varying boundary condition. In this talk, we will present a newly developed numerical solution of the heat transfer equation that utilizes the full implicit method simultaneously for both the differentiation and spatial integration of temperature. The new numerical solution is applicable to the cases of both the single phase above and liquid-vapor coexisting phases below the critical temperature. This new solution is valid for any boundary conditions. In this talk, we demonstrate several case studies for ground-based and microgravity conditions. The special case of an amplified temperature response in the vapor phase when the liquid boundary is subject to an AC temperature oscillation will also be presented. [Preview Abstract] |
Tuesday, March 22, 2005 3:54PM - 4:06PM |
L33.00008: Crossover equation of state for the liquid-vapor critical point Joseph Rudnick, Martin Barmatz, Fang Zhong The principles and implementation of a new crossover equation of state for liquid vapor systems will be presented. The equation of state incorporates crossover that is correct in both the mean field and asymptotic critical regimes. It is also consistent with both leading order and correction-to-scaling amplitude ratios. We discuss the comparison between this equation of state and the results of recent measurements of thermodynamic properties of $^3$He in the vicinity of its liquid-vapor critical point. [Preview Abstract] |
Tuesday, March 22, 2005 4:06PM - 4:18PM |
L33.00009: Kelvon--Phonon Interaction Evgeny Kozik, Boris Svistunov Kelvin waves (kelvons)---the distortion waves on quantized vortex lines---play the key part in the zero- temperature relaxation of superfluid turbulence. The relaxation scenario implies a Kelvin wave cascade, cut off by sound emission. We derive the kelvon--phonon Hamiltonian, thereby reducing the problem of interaction of Kelvin waves with sound to elementary excitation scattering. On the basis of this formalism, we revisit the problem of sound emission by superfluid turbulence. [Preview Abstract] |
Tuesday, March 22, 2005 4:18PM - 4:30PM |
L33.00010: Smoothness and Vortex-Wall Interactions in Superfluid Helium Rena Zieve, Cynthia Frei, Deanna Wolfson We study two aspects of the interaction between a surface and a single vortex line terminating on the surface. One is pinning, when a moving vortex becomes caught at some point on the wall. The second is the energy dissipation as the vortex moves, which appears to be dominated by a vortex-surface interaction. When we reduce the surface roughness through mechanical polishing, we find that the energy loss decreases, as expected if the dissipation comes from a ``friction" force which is weaker for smoother walls. The change is small, about a factor of 3 for several orders of magnitude difference in surface roughness. This is consistent with the very small vortex core size in ${}^4$He since even our highly polished surfaces are ``rough" on the scale of the vortex core. A more surprising finding is that the vortex is {\em more} likely to pin on the smooher walls, suggesting that this vortex-surface interaction is stronger for smoother walls. We will discuss how a mesh of small vortex lengths pinned along the container surface may contribute to these observations. [Preview Abstract] |
Tuesday, March 22, 2005 4:30PM - 4:42PM |
L33.00011: Josephson oscillations in superfluid $^{4}$He Emile Hoskinson, Richard Packard We will describe observations of superfluid oscillations between two samples of $^{4}$He joined by an array of submicron-sized apertures. The fluid oscillates at the Josephson frequency, $f_{j} = \Delta\mu/h$, where $h$ is Plank’s constant and $\Delta\mu$ is the full chemical potential difference, containing both temperature and pressure differences. The oscillations are observed at temperatures sufficiently below the superfluid transition temperature $T_{\lambda}$ that the current phase relation is linear, ie. not sine-like. Evidently the oscillations are the signature of coherent $2\pi$ phase slippage in the array. Work supported in part by grants from the NSF and NASA. [Preview Abstract] |
Tuesday, March 22, 2005 4:42PM - 4:54PM |
L33.00012: Frequency Dependence of Hydrodynamic Inductance in 4He Helmholtz Resonators Talso Chui, Konstantin Penanen The oscillatory motion of helium near the superfluid transition temperature changes from superfluid-only to two-component solid body when viscous length becomes smaller then the flow channel size. In Helmholtz oscillators commonly used to study Josephson effect and related phenomena in helium, the size of the sub-micron apertures is typically smaller than the viscous length, while the size of the macroscopic flow path can be smaller or larger than the viscous length, depending on the frequency used. This opens the possibility that the hydrodynamic inductance ratio of the flow path and the aperture array can be varied. We discuss the implications of this behavior for superfluid SQUID mechanical and thermodynamic stability. [Preview Abstract] |
Tuesday, March 22, 2005 4:54PM - 5:06PM |
L33.00013: Spin Relaxation in Superfluid $^3$He H. Kojima, R. Masutomi, K. Kimura, S. Kobayashi, A. Yamaguchi, H. Ishimoto The spin relaxation time in superfluid $^3$He A$_1$ phase is studied using magnetic fountain pressure techniques. Measurements have been made previously as functions of temperature and pressure. Preliminary measurements will be reported on the dependence of the relaxation time (0.5 $\sim$ 1.5 s) on applied magnetic field (H$_a$) and $^4$He coverage. At low field range of 0.5 $<$ H$_a$ $<$ 1 tesla, the spin relaxation time increases linearly with H$_a$ as expected. Unexpectedly, in the 2 $<$ H$_a$ $<$ 8 tesla range, the relaxation shows little variation. When the interior wall surfaces (including those of heat exchanger) are covered with five layers of $^4$He, surprisingly, the measured relaxation time decreases. [Preview Abstract] |
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