Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session L22: Effects of Geometry on Superfluid Helium |
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Sponsoring Units: DCMP Chair: James Sauls, Northwestern University Room: 202A |
Wednesday, March 4, 2015 8:00AM - 8:12AM |
L22.00001: New Phases Stabilized by Anisotropic Impurity in $^3$He A.M. Zimmerman, J.I.A. Li, J. Pollanen, C.A. Collett, W.P. Halperin We have introduced anisotropic impurity into superfluid $^3$He using well-characterized silica aerogel samples negatively strained by mechanical compression along the cylinder axis by $\approx 10\%$, $20\%$, and $30\%$. Using NMR measurements, we determined the temperature-magnetic field phase diagrams for these amounts of strain. In previous work it was found that in the presence of negative strain of $\approx 20\%$ the superfluid A-phase is only stable above a critical magnetic field, $H_c$.\footnote{ J.I.A. Li {\it et al.}, Phys. Rev. Lett. \textbf{112}, 115303 (2014).} We have found $H_c^2$ increases linearly with strain. By comparing the measured NMR longitudinal resonance frequency to results from unstrained isotropic aerogel, we have determined that in the presence of negative strain the B-phase evolves into a new anisotropic phase. This new anisotropic phase is more stable than the A-phase for fields below $H_c$. This work was supported by the National Science Foundation, DMR-1103625. [Preview Abstract] |
Wednesday, March 4, 2015 8:12AM - 8:24AM |
L22.00002: Puddles of Helium on graphite surfaces Ushnish Ray, Norman Tubman The ground state of $^3He$ in 2D has long been theoretically suspected to be in a non-binding gaseous state. Recent experiments with ultra low density $^3He$ adsorbed on Grafoil have shown, however, that below a critical density ($0.6$ -- $0.9$ $nm^-2$) this 2D system becomes a self bound liquid.\footnote{D. Sato, K. Naruse, T. Matsui and H. Fukuyama, Phys. Rev. Lett {\bf 109}, 235306 (2012)} Subsequent numerical studies with an idealized graphite potential indicate that such a state is forbidden, but can possibly form on other alkali substrates.\footnote{M. Ruggeri, S. Moroni, and M. Boninsegni, Phys. Rev. Lett. {\bf 111}, 045303 (2013)} A key aspect not taken into consideration in such studies are the details of the anisotropic graphite potential. Our studies with finite temperature Path-Integral Monte-Carlo and ground state Diffusion Monte-Carlo techniques that use the full anisotropic graphite potential, on the other hand, reveals an alternate picture. We find that although the effective mass induced by the graphite surface is not enough to induce a macroscopic liquid, the system can still form ultra low density liquid puddles composed of a few $^3He$ atoms. This picture is in agreement with experimental findings and illuminates a novel phase of Helium on graphite surfaces [Preview Abstract] |
Wednesday, March 4, 2015 8:24AM - 8:36AM |
L22.00003: Confinement effect on Anderson-Higgs modes in superfluid $^3$He-B T. Mizushima, J.A. Sauls Superfluid $^3$He is a prototype to observe the spectrum of Anderson-Higgs (AH) modes associated with spontaneous symmetry breaking. In bulk superfluid $^3$He, AH modes have been observed experimentally through attenuation of zero sound, propagation of transverse sound and its acoustic Faraday rotation. Starting from a Lagrangian formulation, we examine the AH modes of $^3$He-B confined in a restricted geometry. For bulk $^3$He-B this formalism leads to the well known spectrum of bosonic collectives modes of the bulk B-phase labelled by the quantum numbers for total angular momentum, $J=0,1,2,\ldots$, the projection along an axis, $J_z=-J,\ldots,+J$, and the parity under particle-hole conversion, $K=\pm 1$. For the equilibrium phases of $^3$He confinement induces pair breaking and leads to symmetry breaking, giving rise to a rich topological phase diagram. In terms of the bosonic excitations, we find that confinement induces symmetry breaking and leads to mixing of modes with different $J$, as well as to level splittings of the AH modes that are otherwise degenerate in bulk $^3$He-B. We find a new spectrum of Bosonic modes is generated that are bound to the surface of superfluid $^3$He in a restricted geometry. We also report on the coupling of the AH modes to ultra-sound. [Preview Abstract] |
Wednesday, March 4, 2015 8:36AM - 8:48AM |
L22.00004: Topological quantum phases of helium-4 confined to nanoporous materials Lode Pollet, Anatoly Kuklov The ground state of $^4$He confined in a system with the topology of cylinder can display properties of solid, superfluid, and liquid crystal. This phase, which we call a compactified supersolid (CSS), originates from wrapping the basal planes of the bulk hcp solid into concentric cylindrical shells, with several central shells exhibiting superfluidity along the axial direction. Its main feature is the presence of a topological defect which can be viewed as a disclination with Frank index $n=1$ observed in liquid crystals, and which, in addition, has a superfluid core. The CSS as well as its transition to an insulating compactified solid with a very wide hysteresis loop are found by ab initio Monte Carlo simulations. A simple analytical model captures qualitatively correctly the main property of the CSS--a gradual decrease of the superfluid response with increasing pressure. [Preview Abstract] |
Wednesday, March 4, 2015 8:48AM - 9:00AM |
L22.00005: $^3$He Condensation and Dissolution at Layer Completion in $^3$He-$^4$He Mixtures Adsorbed on Carbon Nanotubes Gary Williams, Emin Menachekanian, John Abraham, Bob Chen, Vito Iaia, Andrew Li, Sergey Sushchikh The condensation and then dissolution of $^3$He has been observed at layer completion in $^3$He-$^4$He mixtures adsorbed on multiwall carbon nanotubes. With an initial fill of 3.5 layers of $^4$He, the addition of $^3$He in five steps of 0.07 layers uniformly reduces $T_{KT}$, showing that the $^3$He is uniformly distributed. With the final 0.35 layer of $^3$He still present, additional $^4$He is then added at low temperature (225 mK). An abrupt transition is observed in the third sound signal very near the total-thickness 4.0 layer completion, where the Q factor suddenly drops by two orders of magnitude and the sound speed becomes constant. With the addition of another 0.1 layer of $^4$He the sound speed starts to decrease again and the Q climbs back to its initial value. We postulate that this behavior marks the formation of condensed $^3$He ``islands" induced by the layer completion, and then the $^3$He dissolves back to uniform coverage past that point. [Preview Abstract] |
Wednesday, March 4, 2015 9:00AM - 9:12AM |
L22.00006: Dissipative neutral mass flow and quantum phase slips in one dimension Adrian Del Maestro Motivated by experimental progress towards confining bosonic quantum fluids inside nanoscale constrictions, we have determined how quantum phase fluctuations of the superfluid order parameter modify neutral mass transport through a one dimensional channel open to vacuum. In the one dimensional limit, dissipation occurs in the guise of phase slips which may be nucleated due to the presence of impurity scattering, disorder, or a periodic potential. By combining equilibrium quantum Monte Carlo simulations with non-equilibrium calculations in the framework of Luttinger liquid theory, we have computed the relationship between the applied pressure and resistive mass flow for a one dimensional quantum fluid of neutral bosons. Understanding the temperature dependence of the resulting nonlinear pressure-flow behavior may be essential for the interpretation of quasi-1D superfluid flow experiments on helium-4. [Preview Abstract] |
Wednesday, March 4, 2015 9:12AM - 9:24AM |
L22.00007: Glass Microfluidics for Quantum Fluids in Restricted Geometries J. P. Davis, X. Rojas Over the past few years we have developed a suite of measurements based on precisely defined glass microfluidic structures. Such measurements include sound velocity and attenuation in an acoustic analog of a Fabry-Perot cavity [1] and now a superfluid $^4$He nanomechanical Helmholtz resonator [2]. The latter is capable of precisely determining the superfluid density, which will be useful of exploration of Majorana fermions at the surface of $^3$He-B [3], as well as studies of quantum nanomechanical resonators. I will describe our devices and measurements, as well as possible future measurements including studies of quantum turbulence and low-temperature optomechanics [4]. [1] X. Rojas, B. D. Hauer, A. J. R. MacDonald, P. Saberi, Y. Yang and J.P. Davis, Phys. Rev. B 89, 174508 (2014). [2] X. Rojas and J.P. Davis, arXiv:1410.5879 (2014). [3] H. Wu and J. A. Sauls, Phys. Rev. B 88, 184506 (2013). [4] L. A. DeLorenzo and K. C. Schwab, New J. Phys. 16, 113020 (2013). [Preview Abstract] |
Wednesday, March 4, 2015 9:24AM - 9:36AM |
L22.00008: Pressure driven flows of superfluid helium-4 through a single nanopipe Angel Velasco, Zuzanna Siwy, Peter Taborek We have measured flow rates of helium-4 through a single etched nanopore of 31 nm diameter in mica with a mass spectrometer. Flow rates were measured as a function of pressure at constant temperature and at saturated vapor pressures along the coexistence curve between 0.5 K and 3.5 K. Due to the constraint of the mass spectrometer the low pressure side was maintained at P$=$0 creating an intrinsic superfluid/vapor interface which forms inside the pipe or at its exit. We observed two flow regimes at low temperatures with velocities in the range of 6 and 11 m/s consistent with Feynman's vortex critical velocity and a thermal vortex nucleation model respectively. The velocity in a laminar, viscous flow is proportional to the pressure drop while in superfluid flows to zeroth order the velocity is independent of the pressure. A first order correction shows a linear dependence on the pressure with the slope continuously varying from a positive to a negative value near the lambda point. We have also measured flow rates in the normal state and found rates in exact agreement with conventional viscous theory that incorporates the Laplace pressure and a zero slip length[1]. Supported by NSF DMR-0907495. [1] Velasco et al. Appl. Phys. Lett. \textbf{105}, 2014 [Preview Abstract] |
Wednesday, March 4, 2015 9:36AM - 9:48AM |
L22.00009: A titanium transition-edge sensor for the in-situ detection of individual He$_{2}$* excimers in superfluid helium Faustin Carter, Scott Hertel, Catherine Matulis, Michael Rooks, Daniel McKinsey, Daniel Prober Incident radiation can excite superfluid helium into a diatomic He$_{2}$* excimer, which decays through the emission of a 15 eV photon. Such excimers have been used as tracers to measure the superfluid's quantum turbulence, thanks in part to the long half-life of the He$_{2}$* triplet state ($\sim$ 13 seconds). However, the efficient detection of single or a few excimers remains a challenge. We present a detector capable of in-situ detection of the He$_{2}$* excimers either directly (the excimer collides with the detector), or by collecting the 15 eV photon emission upon decay. This detector is based on a titanium superconducting transition-edge sensor (TES), with an energy resolution of 1.5 eV fwhm, coupled to an aluminum absorber. The TES is designed to operate from 20-300 mK in a dilution refrigerator. We will discuss operating characteristics of the detector and present preliminary data for detection of individual excimers. [Preview Abstract] |
Wednesday, March 4, 2015 9:48AM - 10:00AM |
L22.00010: Interaction of Ions, Atoms and Small Molecules with Quantized Vortex Lines in Superfluid $^4$He Jussi Eloranta, David Matteo, Gary Williams The interaction of a number of impurities (H$_2$, Ag, Cu, Ag$_2$, Cu$_2$, Li, He$^+_3$, He$^*$ ($^3S$), He$_2^*$ ($^3\Sigma_u$) and $e^-$) with quantized rectilinear vortex lines in superfluid $^4$He is calculated using density functional methods at 0 K. The technique yields the impurity radius as well as the vortex line core parameter. The core parameter at 0 K (0.74 \AA{}) obtained either directly from the vortex line geometry or from the trapping potential fitting is smaller than previously suggested but is compatible with a re-analysis of the Rayfield-Reif experiment. All of the impurities have significant binding energies to the vortex lines below 1 K where the thermally assisted escape process becomes very inefficient. Even at higher temperatures the trapping times, especially for larger clusters, are sufficiently long that the observed metal nanowire assembly in superfluid helium can take place at vortex lines. The binding energy of the electron bubble is predicted to decrease as a function of both temperature and pressure, which allows adjusting the trap depth for either permanent trapping or thermally assisted escape. A new scheme for determining the trapping of impurities on vortex lines by optical absorption spectroscopy is outlined and demonstrated for He$^*$. [Preview Abstract] |
Wednesday, March 4, 2015 10:00AM - 10:12AM |
L22.00011: Shapes of Swiftly Spinning Superfluid He Nanodroplets Charles Bernando, Rico Tanyag, Curtis Jones, Luis Gomez, Andrey Vilesov, Camila Bacellar, James Cryan, Katrin Siefermann, Felix Sturm, Oliver Gessner, Denis Anielski, Lars Englert, Lutz Foucar, Daniel Rolles, Artem Rudenko, Joachim Ullrich, Robert Hartmann, Martin Huth, Ken Ferguson, Sebastian Schorb, Christoph Bostedt The results of recent measurements of the shapes of large rotating superfluid He nanodroplets of about 500 nm in diameter are presented. The droplets are produced upon expansion of high purity He gas into vacuum through a nozzle at a temperature of 5 K. The droplets were irradiated by the Linac Coherent Light Source X-ray free electron laser to obtain coherent diffraction images of the droplets. Some diffraction images indicate the presence of non-spherical droplets with a large aspect ratio of up to about 2 that possess wheel shapes. A few images also show the existence of droplets with a depression in the middle. These images are attributed to the oblate axisymmetric shapes adopted by fast rotating droplets. The contours of individual droplets are reconstructed using an inverse Fourier Transform and compared with the results of theoretical calculations for classical droplets. The angular velocity in the droplets is estimated. The range of stability of the droplets is analyzed. The experiments and the full list of authors are reported in Science 345, 906 (2014). [Preview Abstract] |
Wednesday, March 4, 2015 10:12AM - 10:24AM |
L22.00012: Helium-3 Confined to a 1.08 Micron Deep Cavity Nikolay Zhelev, Abhilash Sebastian, Lev Levitin, Ben Yager, Andrew Casey, John Saunders, Jeevak Parpia We describe measurements of superfluid Helium-3 confined to a high-aspect ratio cavity within the head of a high quality factor torsion pendulum. The 1.08 $\mu$m deep, rotationally symmetric cavity (11 mm diameter) is defined into a 14 mm diameter silicon disk. The silicon disk is anodically bonded to a matching octagonal glass piece to complete the torsion head. The thickness of 1 mm for both the glass and the silicon ensures minimal distortion of the cavity up to a few bars of pressure. We observe that the normal fluid component stays coupled to the smooth walls of the cavity down to the lowest measured temperatures. By tracking the torsion pendulum frequency and quality factor, we can identify a well defined superfluid transition in the fluid within the pendulum head. We plan to map out the phase diagram for the highly confined Helium-3 at low pressures and observe whether a ``stripe phase'' is realized in the vicinity of the transition between the A and B superfluid phases.\footnote{A.B. Vorontsov and J.A. Sauls, PRL 98, 045301.} [Preview Abstract] |
Wednesday, March 4, 2015 10:24AM - 10:36AM |
L22.00013: The Fermionic spectrum, phase transition and domain walls of confined $^3$He-A film Hao Wu, J. A. Sauls The edge states of a $^3$He-A film are Weyl Fermions propagating on the edge in a direction determined by the chirality of the bulk phase. Under lateral confinement, the wave functions for counter-propagating Weyl Fermions on opposing edges overlap. We show that the edge states hyrbridize and form a band, and the continuum states exhibit band gaps. We report self-consistent calculations of the reduction in the spontaneous edge mass currents due to hybridization as a function of lateral confinement, $D$. Strong lateral confinement leads to a sequence of quantum phase transitions. The A phase undergoes a transition to a pair density wave (PDW) phase with broken translational symmetry at $D_{c_1}\approx 13\xi_0$, and a transition to a polar state at $D_{c_2}\approx 9\xi_0$. The PDW phase for $D < D_{c_1}$ is periodic array of chiral domains separated by domain walls\footnote{Y. Tsutsumi, \textbf{J. Low Temp. Phys.} 175, 2014} with currents that conflict with the direction of edge currents. We report self-consistent calculations of the PDW phase near $D_{c_1}$ that resolves the competition in energy between edge states and Fermions bound to the domain wall. The resulting pattern of circulating currents also resolves the apparent violation of current conser [Preview Abstract] |
Wednesday, March 4, 2015 10:36AM - 10:48AM |
L22.00014: A Variable Path Length Cell for Transverse Acoustic Studies of Superfluid $^3$He C.A. Collett, M.D. Nguyen, J.I.A. Li, A.M. Zimmerman, W.P. Halperin, J.P. Davis Transverse sound has recently emerged as an effective probe of the order parameter of superfluid $^3$He. Both the transverse acoustic impedance\footnote{R. Nomura \textit{et al.}, Physica E \textbf{55}, 42-47 (2014)} and attenuation\footnote{J.P. Davis \textit{et al.}, Nature Physics \textbf{4}, 571-575 (2008)} have been shown to couple to surface bound states in $^3$He-$B$, which are predicted to be Majorana states in the specular scattering limit. In order to measure the attenuation at different path lengths to separate surface from bulk effects, as well as reduce the cavity size to the micron scale where transverse sound propagation should be measurable in the normal state,\footnote{L.D. Landau, Sov. Phys. JETP \textbf{32}, 59 (1957)} we have constructed a variable path length cell. Using a $^4$He-actuated diaphragm we demonstrate in-situ changes to the cavity length at dilution temperatures, and report our progress in deploying the cell at sub-mK temperatures. This research was supported by the National Science Foundation grant DMR-1103625. [Preview Abstract] |
Wednesday, March 4, 2015 10:48AM - 11:00AM |
L22.00015: Micromachined Angle Resolved $^3$He Quasi-particle Detector Yoonseok Lee, C.S. Barquist, P. Zheng, W.G. Jiang, T.R. Schumann, Y.K. Yoon Micromachined comb-drive mechanical resonators have been developed for the study of quantum fluids. Our study in $^3$He-B showed that the temperature dependence of the damping in this device was consistent with a damping model derived from thermal quasi-particles and demonstrated its potential as a sensitive quasi-particle flux detector. It is natural to conceive a scheme to build angle-resolved or space-momentum resolved $^3$He quasi-particle detectors in the form of array of resonators. This type of detectors could play an important role in revealing detailed structure of excitations or visualizing vortices in quantum fluids. A prototype detector is composed of $4 \times 4$ or $6 \times 6$ array of comb-drive resonators with strategically dispersed resonance frequencies. In this paper, We will discuss the working principle and design of the detector array.\\ [Preview Abstract] |
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