Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session S17: Quantum Fluids and Solids II |
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Sponsoring Units: DCMP Chair: Henry Glyde, University of Delaware Room: Morial Convention Center 209 |
Wednesday, March 12, 2008 2:30PM - 2:42PM |
S17.00001: Phonon-roton modes and a Bose glass phase in nanoscale liquid $^4$He Jacques Bossy, Jonathan Pearce, Schober Helmut, Henry Glyde We present neutron scattering measurements of the elementary phonon-roton modes of liquid $^4$He confined in nanoporous media. The aim is to compare phonon-roton (P-R) and superfluid density measurements in helium at nanoscales and in disorder. A specific goal is to determine the region of temperature and pressure in which well defined phonon-roton modes (and therefore BEC) exist and compare this with the superfluid region. In 25 $\AA$ mean pore diameter gelsil Yamamoto et al.[1] find that the superfluid phase extends up to a temperature T$_c$ = 1.4 K at saturated vapor pressure (SVP) (p $\simeq$ 0) and up to a pressure p$_c$ = 34 bar at (T $\simeq$ 0). There is apparently a Quantum Phase Transition at p$_c$ = 34 bar[1]. We find well defined P-R modes (BEC) extend above T$_c$ at SVP (up to T$_\lambda$ = 2.17 K) and to pressures above p$_c$ (up to a pressure p = 36.3-36.8 bars at T $\simeq$ 0 but no modes above this pressure). This suggests that there is a Bose glass phase consisting of local regions of BEC (fragmented BEC) separated by regions with no BEC surrounding the superfluid phase at all p and T. We compare this phase diagram with other dirty Bose systems. [1] Yamamoto et al. Phys. Rev. Lett. 93, 075302 (2004). [Preview Abstract] |
Wednesday, March 12, 2008 2:42PM - 2:54PM |
S17.00002: Elastic transmission of atoms through superfluid $^4$He Yaroslav Lutsyshyn, J. Woods Halley We investigate completely elastic transmission of atoms through a slab of strongly interacting helium superfluid by diffusion Monte Carlo (DMC) method. Both quasiparticle and condensate mediated modes of transmission have been predicted$^{1,2}$ but only quasiparticle mode has been observed$^{3,4}$. We performed numerical calculations of the transmission probability using DMC with a modified fixed-node approach to find the phase shifts of scattering states for elastic transmission process of atoms incident normal to the surface of a free standing helium slab. Transmission coefficients for different energies of the incident atom were computed. Preliminary results for the group velocity of a transmitted wave packet hint at rapid transmission with times characteristic of the virtual condensate mediated process. This work was supported in part by the University of Minnesota Supercomputing Institute. \newline [1] J.~W.~Halley et al., PRL \textbf{71}, 2429 (1993) \newline [2] A.~K.~Setty et al., PRL \textbf{79}, 3930 (1997) \newline [3] K.~A.~Lidke et al., J. Low Temp. Phys. \textbf{140}, 429 (2005) \newline [4] C.~D.~H. Williams et al., PRL \textbf{91}, 085301 (2003) [Preview Abstract] |
Wednesday, March 12, 2008 2:54PM - 3:06PM |
S17.00003: Experimental Observation of Quantized Vortex Reconnection and Turbulence in Superfluid Helium Matthew Paoletti, Katepalli Sreenivasan, Daniel Lathrop We present experimental studies of the first direct visualization of reconnecting quantum vortices and the decay of superfluid turbulence in $^{4}$He. Micron-sized solid hydrogen particles are used for particle tracking. The cores of the superfluid vortices trap the hydrogen particles, thereby allowing direct visualization of the dynamics of the line-like defects. We generate superfluid turbulence by driving a thermal counterflow. After pulsing the counterflow, the system relaxes through a cascade of reconnection events. We examine the dynamics of pairs of particles trapped on reconnecting vortices and observe that these particles separate as power laws in time with a scaling exponent distributed about the predicted value of $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $. We show that reconnection leads to power-law tails in the velocity probability distribution function, which is in stark contrast to the Gaussian tails that are ubiquitous in classical turbulence and thermal motion. [Preview Abstract] |
Wednesday, March 12, 2008 3:06PM - 3:18PM |
S17.00004: ABSTRACT WITHDRAWN |
Wednesday, March 12, 2008 3:18PM - 3:30PM |
S17.00005: Scanning Superfluid-Turbulence Cascade by Its Low-Temperature Cutoff Evgeny Kozik, Boris Svistunov Recent advances in experimental techniques have made it possible to explore highly non-trivial short-wavelength physics of low-temperature superfluid turbulence. We analyze the transformation of the (quasi-)classical Kolmogorov cascade into the Kelvin-wave cascades on individual vortex lines at high enough wavenumbers, revealing a chain of three qualitatively distinct intermediate regimes, supported by local-induction motion of the vortex lines, and distinguished by specific reconnection mechanisms. On the basis of this scenario, we develop a theory of low-temperature cascade cutoff, which predicts a peculiar behavior of the quantized vortex line density, $L$, controlled by the frictional coefficient, $\alpha(T) \ll 1$, responsible for the cutoff. Excellent agreement with a recent experiment by Walmsley {\it et al.} [arXiv:0710.1033]---in which $L(T)$ has been measured down to $T \sim 0.08\,$K---validates our scenario and allows to quantify the Kelvin-wave cascade spectrum. [Preview Abstract] |
Wednesday, March 12, 2008 3:30PM - 3:42PM |
S17.00006: ABSTRACT WITHDRAWN |
Wednesday, March 12, 2008 3:42PM - 3:54PM |
S17.00007: Metastable Composite Vortices in Spinor Condensates Ari Turner, Eugene Demler The ground states of condensates of atoms with spin have a variety of symmetries leading to many types of vortices. The quadratic Zeeman effect produces composite metastable vortices, which are configurations of vortices held together by a force resulting from the Zeeman effect as we explain. If the component vortices were to conbine together and react to form a different set of components, then the composite vortex could break up. However, this is prevented by short-range repulsions. Our analysis focuses on the cyclic phase, where the chemistry of the vortices is regulated by the symmetry group of a tetrahedron. [Preview Abstract] |
Wednesday, March 12, 2008 3:54PM - 4:06PM |
S17.00008: Quantum Monte-Carlo study of a two-band boson Hubbard model Siegfried Guertler, Matthias Troyer, Fu-Chun Zhang We consider a two band boson Hubbard model, in which the on-site interaction is infinity for the intra-band bosons and repulsive for the inter-band bosons. The on-site inter-band boson interaction may facilitate condensation of vacancies of $a$-boson and interstitials of $b$-boson. We report results of large scale quantum Monte Carlo simulations to study possible supersolid phases of the model. [Preview Abstract] |
Wednesday, March 12, 2008 4:06PM - 4:18PM |
S17.00009: A simple model of thermal conductivity in supersolid Helium Joshua Thibodaux, Ilya Vekhter, Matthias Graf, Alexander Balatsky The recent discovery of the decrease of the torsional oscillator period in solid Helium has led to a renewed interest in a supersolid state. The simplest model for this state is one in which the vacancies undergo Bose-Einstein condensation. Within this model we use the Boltzmann equation to investigate the thermal conductivity of normal $^4$He and super solid by considering phonons interacting with a gas of vacancies. We analyze the temperature dependence of the thermal conductivity and specific heat for different vacancy concentrations. We will discuss the consequences of our calculations for existing and future experiments. [Preview Abstract] |
Wednesday, March 12, 2008 4:18PM - 4:30PM |
S17.00010: Local melting at surface and isotope impurities in quantum solids Emmanuele Cappelluti, Gianluca Rastelli, Sergio Gaudio, Luciano Pietronero Surface melting is a well known phenomenon in classical solids, and it can be related to a {\em local} instability of the solid phase close to the surface truncation. In this contriibution we employ a self-consistent harmonic approximation to investigate surface melting and local melting close to quantum impurities in quantum solids. We show that surface melting can occur at temperatures much lower than the critical temperature $T_c$ of the solid phase instability in the bulk. Similar effects are driven by the presence of an isotope substitution. In this latter case, we show that stronger local lattice fluctuations, induced by a lighter isotope atom, can induce local melting of the host bulk phase. Experimental consequences and the possible relevance in solid helium are discussed. [Preview Abstract] |
Wednesday, March 12, 2008 4:30PM - 4:42PM |
S17.00011: A Kosterlitz-Thouless transition in solid $4^$ Helium? Sergio Gaudio, Emmanuele Cappeluti, Gianluca Rastelli, Luciano Pietronero We show that the reproducible ``Non-Classical Rotational Inertia'' signals in solid Helium four are completely ascribable to a Kosterlitz-Thouless transition of liquid $^4$He at the grain boundaries. Despite our toy model, we obtain a surprisingly good agreement with the experimental data when comparing the drop of the momentum of inertia. Within our model, we give an estimate of the average size of the grains, which we argue to be limited by the isotopic impurities and show that the signal is inversely proportional to the size of the average size of the grains. [Preview Abstract] |
Wednesday, March 12, 2008 4:42PM - 4:54PM |
S17.00012: Disorder-induced Missing Moment of Inertia in Solid $^4$He Jiansheng Wu, Philip Phillips A microscopic model for the experimentally observed missing moment of inertia in the torsional oscillator experiments on partially-annealed solid $^4$He is proposed. We argue that an ordered array of $^4$He atoms is a Mott insulator. Disorder destroys the Mott state producing localized states in the gap which beyond a critical value of the disorder induce a superfluid state. Depending on the magnitude of the disorder, we find that the destruction of the Mott state takes place for $d\le 3$ either through a Bose glass phase (strong disorder and weak disorder) or through a direct transition to a superfluid (intermediate disorder).The critical value of the disorder that separates three region of disorder is shown to be a function of the boson filling, interaction and the momentum cut off. We apply our work to the experimentally observed enhancement $^3 $He impurities has on the onset temperature for the missing moment of inertia. We find quantitative agreement with experimental trends. [Preview Abstract] |
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