Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Z22: He3 - He4 Quantum Fluids |
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Sponsoring Units: DCMP Chair: Benjamin Hunt, Massachusetts Institute of Technology Room: 324 |
Friday, March 22, 2013 11:15AM - 11:27AM |
Z22.00001: Chiral Phases of Superfluid $^3$He in an Anisotropic Medium James Sauls I report theoretical results for the phases of superfluid $^3$He infused into homogeneous uniaxial aerogel. Ginzburg-Landau (GL) theory for a class of equal-spin-pairing (ESP) states in a medium with uniaxial anisotropy is developed and used to analyze recent experiments on uniaxially strained aerogels. For $^3$He in an axially ``stretched'' aerogel GL theory predicts a transition from normal liquid into a \emph{chiral} ABM phase in which the chirality axis is aligned along the strain axis. This state is protected from random fluctuations in the anisotropy direction, has a positive NMR shift, a sharp NMR resonance line and is in quantitative agreement with NMR in the high-temperature ESP-1 phase of superfluid $^3$He in axially stretched aerogel. A second transition into a bi-axial phase is predicted to onset at a slightly lower temperature. This phase is an ESP state, breaks time-reversal symmetry, and is defined by an order parameter that spontaneously breaks axial rotation symmetry. The bi-axial phase has a continuous degeneracy associated with broken axial symmetry. Theoretical predictions for the NMR frequency shifts provide an identification of the ESP-2 phase as the bi-axial state, partially \emph{disordered} by random anisotropy (Larkin-Imry-Ma effect). [Preview Abstract] |
Friday, March 22, 2013 11:27AM - 11:39AM |
Z22.00002: Topological current at an interface between superfluid $^3$He A- and B-phases Yasumasa Tsutsumi At a surface of the superfluid $^3$He, the surface Andreev bound state accompanied with edge current emerges due to a topological phase transition. The topological phase transition at the surface is occurred because the superfluid gap of the superfluid $^3$He among topological superfluids is closed at the interface of a topologically trivial vacuum. Since the paring symmetries are different between the superfluid $^3$He A- and B-phases, topological features are quite different between the A- and B-phases. The A-phase is a chiral superfluid with the spontaneous edge mass current while B-phase is a helical superfluid with the spontaneous edge spin current. At an interface between the A- and B-phase, a topological phase transition is also occurred because they belong in a different topological classification . Then, based on the quasiclassical Eilenberger theory, we discuss topological mass and spin current carried by the bound state at an interface between the A- and B-phases. [Preview Abstract] |
Friday, March 22, 2013 11:39AM - 11:51AM |
Z22.00003: Nanofabricated cells for confined $^3$He Nikolay Zhelev, Robert Bennett, Rob Ilic, Jeevak Parpia, Lev Levitin, Andrew Casey, John Saunders We describe methods for fabrication of Silicon-Glass and all-silicon cells with a height specified to be between 100nm and 1100nm, and with areas on the order of cm x cm. These cells need to meet different requirements, including pressure capability to 30 bar with minimal distortion, and surface roughness which can be characterized and modified as needed to alter the transport characteristics of the confined $^3$He. The cells are suitable for NMR and Torsion Oscillator measurements on the superfluid phases of $^3$He. [Preview Abstract] |
Friday, March 22, 2013 11:51AM - 12:03PM |
Z22.00004: Study of Liquid $^{3}$He Films with MEMS Devices Pan Zheng, Miguel Gonzalez, Yoonseok Lee, Ho Bun Chan Liquid $^{3}$He films with thicknesses of 0.75 and 1.25 $\mu$m were established and probed by micro-electro-mechanical (MEMS) resonators each of which consists of a pair of parallel plates with a well defined separation. The mechanical resonances of the devices immersed in liquid $^{3}$He were studied in a wide range of temperatures from 10 to 800 mK and at sample pressures of 3, 21, and 29 bar. A crossover from Fermi liquid to classical fluid was observed on warming. In the Fermi liquid regime, the damping coefficient associated with the film exhibits an unexpected temperature dependence below 100 mK. This work demonstrates the capacity of MEMS devices as sensitive probes suitable for the study of quantum fluids in a micrometer scale. [Preview Abstract] |
Friday, March 22, 2013 12:03PM - 12:15PM |
Z22.00005: Spin and mass currents on the surface of the topological superfluid, $^3$He-B Hao Wu, James Sauls The surface excitation spectrum of superfluid $^3$He-B is discussed for a translationally invariant interface (specular surface). We report calculations of surface spectral spin-current and mass current densities originating from the Andreev bound state and the continuum response. Two branches of gapless Fermions, bound to the surface, disperse linearly with momentum $\vec{p}_\parallel$ along the surface. These states are spin polarized transverse to their direction of propagation, $\vec{p}_\parallel$. The spectral functions reveal the subtle role of the spin-polarized surface states in relation to the ground-state spin current. By contrast, these states do not contribute to the ground-state mass current density. However, the surface states do give rise to a power law suppression of the superfluid mass current for $0 \ll T \ll T_c$, providing a direct signature of the Majorana branches of surface excitations in the fully gapped 3D topological superfluid, $^3$He-B. [Preview Abstract] |
Friday, March 22, 2013 12:15PM - 12:27PM |
Z22.00006: Observation of the Larkin-Imry-Ma Effect in Superfluid $^3$He-A in Aerogel J.I.A. Li, J. Pollanen, A.M. Zimmerman, C.A. Collett, W.J. Gannon, W.P. Halperin It was proposed by Volovik that $^3$He-A in aerogel will be a superfluid glass owing to the Larkin-Imry-Ma (LIM) effect where arbitrarily small amounts of disorder can disrupt long range directional coherence of a vector order parameter in a condensed system. Several reports of NMR experiments in $^3$He-A have been interpreted as evidence for this phenomenon. However it is not trivial to distinguish the LIM effect induced from disorder on a microscopic scale from macroscopic non-uniformity or anisotropy in the aerogel sample. Order parameter disorder from these two possible mechanisms have very different distributions of order parameter orientations directly observable in the width of the NMR spectrum. If a complete LIM effect is operative there should be no contribution to the line width, contrary to previous reports. On warming from the low temperature isotropic state, we find NMR spectrum shifts characteristic of the dipole-locked axial state, i.e. no sign of a LIM superfluid glass. However, on cooling from the normal state this same phase is fully disordered in a LIM state. We will discuss the origin of the different order parameter structures in superfluid $^3$He-A that result when prepared from the normal state, as compared with warming from the B-phase. [Preview Abstract] |
Friday, March 22, 2013 12:27PM - 12:39PM |
Z22.00007: Phase transitions and critical currents in superfluid $^3$He films Anton Vorontsov, James Sauls Using the quasiclassical theory of superfluidity we investigate thermodynamic and transport properties of superfluid $^3$He in confined geometries. Classic flow experiments, as well as more recent NMR and flow experiments on superfluidity in slab and film geometries, exhibit inconsistencies between experimental results and existing theoretical models of confinement effects. In order to explain the origin of some of these inconsistencies we describe a theoretical model for confinement effects based on scattering of quasiparticles from rough surfaces that is more general than the `specular' and `diffusive' scattering models. Using the this more general boundary scattering model we report theoretical results for (a) the suppression of the superfluid critical temperature $T_c^{film}$, (b) the confinement-driven transition between A and B phases, $T_{AB}$, and (c) effects of the surface roughness on the critical current. The new scattering model should provide a more complete framework for analysis of the properties of confined superfluid $^3$He. [Preview Abstract] |
Friday, March 22, 2013 12:39PM - 12:51PM |
Z22.00008: Unusual Behavior of a MEMS Resonator in Superfluid $^{4}$He Miguel Gonzalez, Pan Zheng, Byoung Hee Moon, Erik Garcell, Yoonseok Lee, Ho Bun Chan Mechanical resonators based on micro-electro-mechanical systems (MEMS) technology were developed for the study of superfluid $^{4}$He [1]. The MEMS device is composed of a movable plate (200 $\times$ 200 $\mu$m$^{2})$ suspended above the substrate by four serpentine springs. The suspended plate moves parallel to the substrate while maintaining a uniform gap between them. A specific device with a 1.25 $\mu$m gap was tested in the superfluid phase of $^{4}$He down to 100 mK. The device exhibits an extreme sensitivity to the excitation level below 400 mK, displaying a nonlinear and hysteretic behavior accompanied by switching. This phenomenon might be related to quantum turbulence generated by a rather simple oscillating plate.\\[4pt] [1] M. Gonzalez, B. Moon, P. Zheng, E. Garcell, H. B. Chan, and Y. Lee. \textit{Journal of Low Temperature Physics, Online First}$^{TM}$\textit{, 22 August 2012}, DOI: 10.1007/s10909-012-0682-8. [Preview Abstract] |
Friday, March 22, 2013 12:51PM - 1:03PM |
Z22.00009: Superfluid helium-4 in one dimensional channel Duk Y. Kim, Samhita Banavar, Moses H. W. Chan, John Hayes, Pier Sazio Superfluidity, as superconductivity, cannot exist in a strict one-dimensional system. However, the experiments employing porous media showed that superfluid helium can flow through the pores of nanometer size. Here we report a study of the flow of liquid helium through a single hollow glass fiber of 4 cm in length with an open id of 150 nm between 1.6 and 2.3 K. We found the superfluid transition temperature was suppressed in the hollow cylinder and that there is no flow above the transition. Critical velocity at temperature below the transition temperature was determined. Our results bear some similarity to that found by Savard {\it et. al.} [1] studying the flow of helium through a nanohole in a silicon nitrite membrane.\newline [1] M. Savard, G. Dauphinais, and G. Gervais, Phys. Rev. Lett. {\bf107}, 254501 (2011) [Preview Abstract] |
Friday, March 22, 2013 1:03PM - 1:15PM |
Z22.00010: Effect of Helium on Vycor Glass: Anomalous Thermal Conductivity Reduction Zhigang Cheng, Samhita Banavar, Moses H. W. Chan There is a long history of studying helium adsorbed in Vycor. In this talk we present the results showing that helium can have a profound effect on the thermal conductivity property of Vycor glass. Although the thermal conductivity of liquid $^4$He is four orders of magnitude higher than that of Vycor, the filling of liquid $^4$He inside the Vycor pores brings about a three-fold reduction of the thermal conductivity as compared with empty Vycor between 0.06 and 0.5 K. By comparing these results with that of superfluid films, liquid $^3$He and solid helium in the Vycor pores, we found that heat is conducted primarily through the silica network even when the pores are filled with solid or liquid helium. The dramatic reduction is brought about by the presence of slow sound mode in liquid $^4$He that greatly facilitates the quantum tunneling of the two level systems (TLS) in the silica which enhances the scattering of the thermal phonons. [Preview Abstract] |
Friday, March 22, 2013 1:15PM - 1:27PM |
Z22.00011: Observation of a New Casimir Effect in Saturated Superfluid $^4$He Films John Abraham, Gary Williams, Konstantin Penanen We report the results of experiments on saturated superfluid $^4$He films in the vicinity of the bulk superfluid transition temperature $T_\lambda$, measuring the film thickness with a capacitance technique and the superfluid density with third sound. For moderately slow temperature sweep rates (0.5 mK/hr) we measure the critical Casimir film-thinning effect with good resolution, and find that the Kosterlitz-Thouless superfluid onset in the film occurs just at the start of the dip in film thickness. When warming through $T_\lambda$ at extremely slow rates (a few $\mu$K/hr), however, we have observed a sudden large increase in the film thickness (nearly 25 {\AA} in a film initially 480 {\AA} thick) within microkelvins of $T_\lambda$. We propose that this is a new type of Casimir effect arising from the viscous suppression of second sound modes in the film, leading to a large free energy difference in the superfluid state that disappears abruptly when second sound ceases to propagate in the bulk helium at $T_\lambda$. [Preview Abstract] |
Friday, March 22, 2013 1:27PM - 1:39PM |
Z22.00012: Cubic interactions in superfluid $^4$He Bjorn F{\aa}k, Thomas Keller, Michael Zhitomirsky, Alexander Chernyshev High-resolution neutron resonance spin-echo measurements of superfluid $^4$He show that the roton energy does not have the same temperature dependence as the inverse lifetime, in contrast to the Landau-Khalatnikov theory. We present a diagrammatic analysis that attributes this effect to the interaction of rotons with thermally excited phonons via both four- and three-particle processes, the latter being allowed by the broken gauge symmetry of the Bose condensate. [Preview Abstract] |
Friday, March 22, 2013 1:39PM - 1:51PM |
Z22.00013: Photon-Roton Modes in Liquid $^4$He coexist with Bose-Einstein Condensation Henry R. Glyde, Jacques Bossy, Jacques Ollivier, Helmut Schober We present neutron scattering measurements of the phonon-roton (P-R) and layer modes of liquid $^4$He confined in MCM-41 under pressure up to 38 bar. The data shows unambiguously that the P-R mode exists at low temperature only. As temperature is increased there is a gradual transfer of intensity from the P-R mode to the normal liquid response, which lies at a lower energy at higher pressure. The transfer takes place with no observable mode broadening. The loss of P-R modes is identified with the loss of Bose-Einstein condensation (BEC). The mode giving rise to the specific heat, $c_V$, of liquid $^4$He in porous media (e.g. gelsil) at higher temperature is the layer mode since the energy of the mode extracted from $c_V$ and the layer mode energy are the same. [Preview Abstract] |
Friday, March 22, 2013 1:51PM - 2:03PM |
Z22.00014: Helium-4 crossover from a 3d superfluid to a 1d Luttinger liquid in a nanopore Bohdan Kulchytskyy, Adrian Del Maestro, Guillaume Gervais Quantum Monte Carlo studies of helium-4 below the bulk superfluid transition temperature show that when it is confined to flow in narrow cylindrical pores with nanometer radii, it tends to form concentric shells around a possible inner core. The latter potentially represents an experimental playground for exploring the implications of Luttinger liquid theory for one dimensional quantum fluids. We have performed large scale numerical simulations investigating the crossover from a bulk three dimensional superfluid to a one dimensional Luttinger liquid as the nanopore radius is reduced at low temperature. Measurements of the superfluid density employing both stiffness and angular momentum estimators provide new insights into confinement induced fluctuation effects in strongly interacting quantum fluids. [Preview Abstract] |
Friday, March 22, 2013 2:03PM - 2:15PM |
Z22.00015: Metastable pin sites for a superfluid vortex Rena Zieve, Ingrid Neumann Circulation trapped around a straight, fine wire can be detected through its effect on the wire's vibration. Here we use such a wire in a cylindrical cell to examine pinning of a superfluid helium vortex line at a macroscopic bump. Hydrodynamic considerations imply that, as long as the fluid velocity is fixed and not too large, a vortex can pin at a unique place on the bump. However, for two separate geometries we find that the vortex has metastable locations both at the apex of the bump and near its edge. In one case, the vortex is trapped around the wire, which terminates in the center of a bump on the cylinder endcap. We find that the vortex can follow the entire length of the wire to the bump apex, or it can leave the wire and make its way through the fluid to the edge of the bump. The former situation is more stable, but the latter can also persist for long times. The second geometry involves a free vortex that extends from the wire to a bump on the cylindrical wall of the container. Again our measurements show pinning at multiple sites on the bump. Interaction of the vortex with the surface curvature may produce the unexpected additional pin sites. [Preview Abstract] |
Friday, March 22, 2013 2:15PM - 2:27PM |
Z22.00016: Recent Progress in Low-Temperature Research from the Davis Lab at the University of Alberta John P. Davis, Xavier Rojas, Yikai Yang, Andrej Duh, Greg Popowich In this talk I will briefly describe our recent progress towards new low-temperature experiments at the University of Alberta in the Davis Lab. We are currently setting up two nuclear demagnetization fridges - one new cryostat that has two independent 9 T magnets (the second magnet being useful for a double demag stage or combined high field and low temperature experiments). The other fridge is an older unit that is extensively refurbished, with all new pumping systems. We are planning numerous experiments at the intersection of low-temperature physics and nanoscience, including quantum properties of nanomechancial resonators and quantum fluids in confined geometries. Concerning the latter, we have fabricated high quality microfluidic devices suitable for low-temperature research. We will discuss our progress towards quantum fluids measurements using these devices. [Preview Abstract] |
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