Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session H33: Quantum Fluids and Solids I |
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Sponsoring Units: DCMP Chair: Norbert Mulders, University of Delaware Room: LACC 511C |
Tuesday, March 22, 2005 8:00AM - 8:12AM |
H33.00001: Mobility of solid 4He James Day, John Beamish Recent torsional oscillator measurements [1,2] on solid $^{4}$He in the pores of Vycor and in bulk demonstrated non-classical rotational inertia and showed a decrease in period below about 200 mK, suggestive of a transition to a supersolid phase. It becomes interesting to see whether solid $^{4}$He exhibits any of the other unusual flow properties of a superfluid. We have performed capacitive measurements on the mobility of solid $^{4}$He in Vycor. By suddenly increasing the pressure in a cell containing a Vycor sample, we were able to monitor the pressure induced flow of solid $^{4}$He in the pores. Near its melting temperature the solid $^{4}$He does flow in/out of the pores, but the flow rate decreases rapidly with temperature, until no flow is observable below 700 mK. We do not see any flow at temperatures down to 25 mK, implying that either supersolid $^{4}$He in Vycor does not flow in response to a large pressure difference or that superflow occurs at a rate far slower than the critical velocities observed by Kim and Chan. We have also begun work on pressure induced flow of bulk solid $^{4}$He. This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC). 1. E. Kim and M.H.W. Chan, Nature 427, 225 (2004). 2. E. Kim and M.H.W. Chan, Science 305, 1941 (2004). [Preview Abstract] |
Tuesday, March 22, 2005 8:12AM - 8:24AM |
H33.00002: A Torsional Oscillator Study of Solid Hydrogen Anthony Clark, Xi Lin, M.H.W. Chan Since the observation of superflow in solid $^{4}$He, we have become interested in duplicating this phenomenon in other systems. In Kim and Chan's original work, trace amounts of $^{3}$He, on the order of parts per million, were added to the system and found to significantly affect the transition. However, there is an altogether different system that is perhaps less complicated, and may also exhibit superflow. On the basis of the de Boer parameter, the most quantum solid other than the helium isotopes, is that of hydrogen. Thus, we have begun a torsional oscillator study of solid H$_{2}$ from dilution temperatures up to the triple point. Solid samples are formed by first filling the torsion bob with liquid H$_{2}$ at $\sim $14K, where the H$_{2}$ has already passed through ortho-para conversion chambers at 50K and 20K. The cell is then gradually cooled to the base temperature of our $^{3}$He-$^{4}$He dilution refrigerator. We present our preliminary data of the resonant oscillation period as a function of temperature. [Preview Abstract] |
Tuesday, March 22, 2005 8:24AM - 8:36AM |
H33.00003: On the Supersolid State of Matter Boris Svistunov, Nikolay Prokof'ev We prove that the necessary condition for a solid to be also a superfluid is to have zero-point vacancies, or interstitial atoms, or both, as an integral part of the ground state. As a consequence, superfluidity is not possible in commensurate solids which break continuous translation symmetry. We discuss recent experiment by Kim and Chan [Nature, {\bf 427}, 225 (2004)] in the context of this theorem, question its bulk supersolid interpretation, and offer an alternative explanation in terms of superfluid helium interfaces. [Preview Abstract] |
Tuesday, March 22, 2005 8:36AM - 8:48AM |
H33.00004: Off Diagonal Long Range Order in Low Temperature Solid Helium Bryan Clark, David Ceperley Experiments have recently produced evidence of the existence of a supersolid $^{4}He$. One of the important properties of equilibrium superfluid/supersolid behavior is the existence of off diagonal long range order, defined in terms of the 1-body density matrix as $\lim_{\left|r-r'\right|\rightarrow\infty}\rho\left(r,r'\right)>0$ . Using path integral monte carlo, we calculate the off diagonal density matrix for solid $^{4}He$ at temperatures near the experiment and find it is very small at large $r$. [Preview Abstract] |
Tuesday, March 22, 2005 8:48AM - 9:00AM |
H33.00005: Superflow in Solid $^4$He Wayne Saslow Kim and Chan have recently observed Non-Classical Rotational Inertia (NCRI) for solid $^4$He in Vycor glass, porous gold, and bulk. Using a microscopic theory where each atom has the same local superfluid velocity (which depends on the microscopic atomic mass density), we show that their low $T$ value of the superfluid fraction, $\rho_{s}/\rho_{0}\approx0.015$, is consistent with what is known of atomic delocalization in this system. In the macroscopic theory, we explicitly include a lattice mass density $\rho_{L}$ distinct from the normal fluid density $\rho_{n}$, thus making the superfluid hydrodynamics consistent with Galilean transformations, which implies that $\rho_{0}=\rho_{s}+\rho_{n}+\rho_{L}$. We also show that $\rho_{L}(T)=\rho_{0}(T)-\rho^{*}_{s}(T)$, where $\rho_{0}(T)$ is the average mass density and $\rho^{*}_{s}(T)$ is computed from the microscopic mass density. This added complexity makes determination of $\rho_{n}/\rho_{0}$ from the measured $\rho_{s}/\rho_{0}$ non-trivial, although an excitation energy of about 0.35~K is relevant as $\rho_{n}/\rho_{0}$ rises from its low temperature value of zero. The macroscopic phase inferred from the observation of NCRI suggests quantum vortices, whose cores must reside between the lattice sites. [Preview Abstract] |
Tuesday, March 22, 2005 9:00AM - 9:12AM |
H33.00006: Superfluid interfaces in quantum solids Evgeni Burovski, Evgeni Kozik, Anatoly Kuklov, Nikolay Prokof'ev, Boris Svistunov One scenario for the non-classical moment of inertia of solid $^4$He discovered by Kim and Chan [{\it Science}, {\bf 305}, 1941 (2004)] is the superfluidity of micro-crystallite interfaces. On the basis of the most simple model of a quantum crystal---the checkerboard lattice solid---we show that the superfluidity of interfaces between solid domains can exist in a wide range of parameters. At strong enough inter-particle interaction, a superfluid interface becomes an insulator via a quantum phase transition. Under the conditions of particle-hole symmetry, the transition is of the standard $U(1)$ universality class in $d=3 $, while in $d=2$ the onset of superfluidity is accompanied by the interface roughening, driven by fractionally charged topological excitations. [Preview Abstract] |
Tuesday, March 22, 2005 9:12AM - 9:24AM |
H33.00007: Premelting Induced Decoupling as a cause of Nonclassical Rotational Inertia in Solid $^4$He J.S. Wettlaufer, J.G. Dash Recent reports by Kim and Chan describe the observation of nonclassical rotational inertia in solid $^4He$, which is taken to demonstrate superfluidity of the solid. This exciting possibility was noted as a long standing speculation, based on the hypothesis of Bose-Einstein condensation of zero-point vacancies. Here we suggest an alternative explanation of the experiment: decoupling of the solid from the wall of the container by grain boundary premelting. However, the premelting in question is not at ordinary grain boundaries, but at the interface between the bulk solid and dense adsorbed layers at the container wall. The dense layers, due strong adsorption forces, are responsible for nonzero wetting angles between solid $^4He$ and copper and glass walls; the contacting surface in question more nearly resembles the interface between two different materials. In view of the sensitivity of premelting to the crystal structure of the solid, and the density difference between the solid and the adsorbed layers at the wall, we propose that premelting occurs at that interface. The reduction in the latent heat of fusion with decreasing temperature enhances the film thickness, which we calculate as function of the parameters of the Lennard-Jones potential to be nearly four atomic layers at the experimental temperatures of 175 mK. [Preview Abstract] |
Tuesday, March 22, 2005 9:24AM - 9:36AM |
H33.00008: Superfluidity of Dense $^4$Helium in Vycor Saad Khairallah, David Ceperley We calculate properties of a model of $^4$He in Vycor using the Path Integral Monte Carlo method to understand the recent experiments of Kim and Chan. In particular we calculate both the density and the superfluid response in the layers immediately above a rough vycor surface. In the second and third layers above the vycor, there is small but not insignificant delocalization caused by the strong density gradient and resulting incommensurate lattice structure. We also find that $^{3}$He impurities tend to populate these layers, which reduces the superfluid density as is found in the experiment. Our results are consistent with the persistent liquid layer model to explain the observations. [Preview Abstract] |
Tuesday, March 22, 2005 9:36AM - 9:48AM |
H33.00009: Exchange Frequencies in Helium-4 Crystals with Defects Burkhard Militzer The torsional oscillator experiments by Kim and Chan indicate the presence of a superfluid flow in solid helium-4 [Science 305 (2004) 1941], which cannot be explained with the properties of a perfect h.c.p. lattice [Ceperley, Bernu, PRL 93 (2004) 155303]. Using \urllink{path integral Monte Carlo}{http://militzer.gl.ciw.edu} simulations, we study different types of defects and stacking faults in the crystal by analyzing the frequency of ring-exchanges along the defect lines. This focus lies on identifying a mechanism that could explain the observed 1\% superfluid fraction. [Preview Abstract] |
Tuesday, March 22, 2005 9:48AM - 10:00AM |
H33.00010: Exactly Soluble Model for Superfluid Solid? Chia-Ren Hu N bosons in a harmonic trap and interacting with each other via a pair-wise repulsive harmonic force is an exactly soluble problem. Could it be an exactly soluble model for superfluid solid? At least the Bose- Einstein condensation of this interacting N-boson system is a fundamentally interesting problem even if it turns out to be only an interacting superfluid. At least the interaction strength can take any value between zero and an upper limit for stability, which would correspond to a strongly interacting system. I have not pushed this problem far enough to state any conclusion here, since the problem is conceived only very recently, but whatever I can find before the meeting time will be reported at the meeting. At least for low N values and/or at T = 0 some results can definitely be obtained, but whether they can be generalized to arbitrary N and finite temperature is unknown at the moment. [Preview Abstract] |
Tuesday, March 22, 2005 10:00AM - 10:12AM |
H33.00011: Construction of an ultra low temperature cryostat at University of Florida P. Bhupathi, H.C. Choi, J. Cancino, Y. Lee We designed, constructed and tested an ultra low temperature Cryostat. The cryostat is equipped with an Oxford Kelvinox 400 dilution refrigerator and a copper nuclear demagnetization stage. The nuclear stage consists of 48 moles of copper connected to the mixing chamber through an indium heat switch. The whole system is mounted on a vibration isolated structure and the main pumping lines have various stages of mechanical filters and dampers. An automated melting pressure thermometer (MPT) was built and employed to measure the temperature. Details of design, construction of the cryostat and results of test are discussed. [Preview Abstract] |
Tuesday, March 22, 2005 10:12AM - 10:24AM |
H33.00012: Potential low cost, safe, high efficiency propellant for future space program D. Zhou, N.S. Sullivan Mixtures of nanometer or micrometer sized carbon powder suspended in hydrogen and methane/hydrogen mixtures are proposed as candidates for low cost, high efficiency propellants for future space programs. While liquid hydrogen has low weight and high heat of combustion per unit mass, because of the low mass density the heat of combustion per unit volume is low, and the liquid hydrogen storage container must be large. The proposed propellants can produce higher gross heat combustion with small volume with trade off of some weight increase. Liquid hydrogen can serve as the fluid component of the propellant in the mixtures and thus used by current rocket engine designs. For example, for the same volume a mixture of 5{\%} methane and 95{\%} hydrogen, can lead to an increase in the gross heat of combustion by about 10{\%} and an increase in the I$_{sp }$(specific impulse) by 21{\%} compared to a pure liquid hydrogen propellant. At liquid hydrogen temperatures of 20.3 K, methane will be in solid state, and must be formed as fine granules (or slush) to satisfy the requirement of liquid propellant engines. [Preview Abstract] |
Tuesday, March 22, 2005 10:24AM - 10:36AM |
H33.00013: A Superfluid Clock Konstantin Penanen, Talso Chui The performance of clocks is limited by the characteristics of the underlying oscillator. Both the quality factor of the oscillator and the signal-to-noise ratio for the resonator state measurement are important. A superfluid helium Helmholtz resonator operating at $\sim $100mK temperatures has the potential of maintaining frequency stability of 5x10$^{-15}$/t$^{1/2}$~ The high dynamic range of lossless SQUID position displacement measurement, and low losses associated with the superfluid flow, combined with high mechanical stability of cryogenic assemblies, contribute to the projected stability. Low overall mass of the assembly allows for multiple stages of vibration isolation. [Preview Abstract] |
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