Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session S47: Low Temperature Properties of He3 |
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Sponsoring Units: DCMP Chair: William Halperin, Northwestern University Room: Mile High Ballroom 4F |
Thursday, March 6, 2014 8:00AM - 8:12AM |
S47.00001: Engineering superfluid $^3$He phase stability with disorder J.I.A. Li, A.M. Zimmerman, J. Pollanen, C.A. Collett, W.J. Gannon, W.P. Halperin We report our NMR measurements on $^3$He superfluid in well-characterized aerogel samples, with anisotropy induced by uniaxial compression of $\approx 20\%$. By comparing with our previous work on the same sample without compression, we show that a critical field appears in the $T$-$H^2$ phase diagram induced by the aerogel anisotropy, providing clear evidence that anisotropic impurity scattering modifies the relative phase stability of different $p$-wave superfluid state, making the isotropic B-phase energetically more favorable than the magnetic field induced A-phase. Furthermore, we demonstrate that the 3-dimensional glass phase of $^3$He-A observed in the isotropic aerogel is suppressed by the anisotropic disorder, and the remaining 2-D continuous symmetry in the plane perpendicular to the strain axis gives rise to a 2-D glass phase of $^3$He-A, contrary to the expected 1-D alignment of the A-phase texture along the strain axis. [Preview Abstract] |
Thursday, March 6, 2014 8:12AM - 8:24AM |
S47.00002: A Variable Path Length Cell for Transverse Acoustic Studies of Superfluid $^3$He C.A. Collett, J.I.A. Li, A.M. Zimmerman, W.J. Gannon, W.P. Halperin Transverse acoustic cavities have recently been shown to provide a probe for the surface bound states of superfluid $^3$He-$B$.$^1$ These states are predicted to have Majorana characteristics in the specular scattering limit. We have developed an acoustic cavity which allows continuous in-situ variation of the path length in order to more fully explore the surface states and to quantify the relative attenuation observed from bulk and surface helium. The variable path length cavity will also allow us to reduce the cavity length down to several microns, sufficient to search for propagating transverse sound modes in the normal state, as predicted by Landau.$^2$ We report the progress we have made in constructing and implementing this new sample cell. \par \medskip \noindent 1. J.P. Davis {\it et al.}, Nature Physics {\bf 4}, 571-575 (2008). \par \noindent 2. L.D. Landau, Sov. Phys. JETP {\bf 32}, 59 (1957). [Preview Abstract] |
Thursday, March 6, 2014 8:24AM - 8:36AM |
S47.00003: Enhanced Methanol Diffusion in Homogeneous Isotropic and Anisotropic Silica Aerogels Jeongseop Lee, A.M. Mounce, Sangwon Oh, A.M. Zimmerman, W.P. Halperin It has recently been shown that chiral superfluid $^3$He states can be stabilized using stretched, anisotropic, high porosity silica aerogel.\footnote{New Chiral Phases of Superfluid $^3$He Stabilized by Anisotropic Silica Aerogel, J. Pollanen, et al., Nature Physics 8, 317 (2012).} We present a novel approach to characterize the aerogel structure using nuclear magnetic resonance measurement of the enhanced diffusion of methanol vapor, similar to previous reports of diffusion of water in partially filled porous glass.\footnote{Enhanced Self-Diffusion of Water in Restricted Geometry, F. D'Orazio, et al., Phys. Rev. Lett. 63, 43 (1989).} The diffusion coefficient is determined by the molecular motion in the vapor phase in fast exchange with adsorbed phase. Consequently, the diffusion is enhanced by two orders of magnitude beyond that of the bulk fluid but is limited by the elastic mean free path $\lambda$ for ballistic molecular motion in the aerogel. The mean free paths in the presence of global anisotropy in a stretched (radially shrunken) aerogel, were found to be larger in the direction of strain by an amount consistent with the strain amplitude measured independently. [Preview Abstract] |
Thursday, March 6, 2014 8:36AM - 8:48AM |
S47.00004: Torsion Pendulum Experiments with Superfluid $^3$He in ``Nematically Ordered'' Aerogel Nikolay Zhelev, Eric Smith, Abhilash Sebastian, Jeevak Parpia A new type of highly anisotropic alumina aerogel [1] is used to induce directional disorder in superfluid $^3$He. The aerogel sample consists of a network of long strands that have a preferred orientation (nematic order). It is placed in the head of a double torsion pendulum with the anisotropy axis oriented along the axis of the pendulum. We observe the frequency shift of the symmetric torsion mode of the pendulum in order to determine the superfluid fraction of the embedded $^3$He. The superfluid transition temperature of the fluid in the aerogel is measured to be very close to that of bulk $^3$He. However, in contrast to the bulk phase diagram, the region of stability of the Equal Spin Pairing (ESP) superfluid phase is enhanced on cooling. In addition, unlike the case of $^3$He in isotropic silica aerogel, the ESP phase reappears on warming. We compare our measurements to the NMR data reported in [2] and discuss the possible structure of the observed superfluid phases. \newline \newline [1] R.Sh. Askhadullin, et.al, J. Phys.: Conf. Ser. 98, 072012 (2008). \newline [2] R.Sh. Askhadullin, et.al, JETP Lett. 95, 326 (2012 [Preview Abstract] |
Thursday, March 6, 2014 8:48AM - 9:00AM |
S47.00005: Ultrasound Attenuation in Normal Fluid $^{3}$He in 98\% Aerogel: Knudsen-to-Hydrodynamic Crossover Yoonseok Lee, H.C. Choi, B.H. Moon, N. Masuhara, M.W. Meisel, H. Takeuchi, S. Higashitani, K. Nagai, N. Mulders Mass flow in porous media is a widely occurring phenomenon as in water flow in aquifers, blood flow in vessels, and petroleum flow through sandstones. However, the understanding of these phenomena is a challenging task. In particular, when the mean free path of the fluid particles exceeds the pore size, the hydrodynamic description breaks down and the fluid mass is carried by the Knudsen diffusion. The $^{3}$He-aerogel system offers an opportunity that allows a systematic investigation of a wide range flow phenomena from the hydrodynamic to Knudsen regime owing to the strongly temperature dependent mean free path in liquid $^{3}$He at low temperatures. In this paper, we present ultrasound attenuation measurements of liquid $^{3}$He in 98\% aerogel. The Knudsen-hydrodynamic crossover is clearly demonstrated in a drastic change in the temperature dependence in attenuation observed in this system. \\ H. Takeuchi {\it et al.,} Phys. Rev. Lett. {\bf 108}, 225307 (2012). [Preview Abstract] |
Thursday, March 6, 2014 9:00AM - 9:12AM |
S47.00006: 2D Larkin-Imry-Ma state of deformed ABM phase of superfluid $^3$He in ``ordered'' aerogel Vladimir Dmitriev, Andrey Senin, Alexey Yudin We report NMR studies of high temperature superfluid phase of $^3$He in so called ``ordered'' aerogel$^1$ which strands are almost parallel to each other. Previously, it was found that the NMR properties of this phase depend on whether it is obtained on cooling from the normal phase or on warming from the low temperature phase$^2$. These two types of high temperature phase (called as ESP1 and ESP2) correspond to Anderson-Brinkman-Morel (ABM) phase with large polar distortion and with orbital vector being in 2D Larkin-Imry-Ma (LIM) state. Here we present results which show that the observed difference in NMR signatures of the ESP1 and the ESP2 states is due to that the corresponding 2D LIM states can be anisotropic. In the ESP1 phase the anisotropy is absent or small, while in the ESP2 phase the anisotropy is large. NMR data have allowed us to estimate values of these anisotropies. \\[4pt] $^1$The aerogel sample was produced by R.Sh. Askhadullin, P.N. Martynov and A.A. Osipov (Leypunsky Institute for Physics and Power Engineering, Obninsk, Russia) \\[0pt] $^2$R.Sh. Askhadullin, V.V. Dmitriev, D.A. Krasnikhin, et al., {\it JETP Lett.} {\bf 95}, 326 (2012) [Preview Abstract] |
Thursday, March 6, 2014 9:12AM - 9:24AM |
S47.00007: Effect of Aerogel Anisotropy in Superfluid $^3$He-A A.M. Zimmerman, J.I.A. Li, J. Pollanen, C.A. Collett, W.J. Gannon, W.P. Halperin Two theories have been advanced to describe the effects of anisotropic impurity introduced by stretched silica aerogel on the orientation of the orbital angular momentum $\hat{l}$ in superfluid $^3$He-A. These theories disagree on whether the anisotropy will orient $\hat{l}$ perpendicular\footnote{G. E. Volovik, J. Low Temp. Phys. \textbf{150}, 453 (2008).} or parallel\footnote{J. A. Sauls, arXiv:1307.7656.} to the strain axis. In order to examine this question we have produced and characterized a homogeneous aerogel sample with uniaxial anisotropy introduced during growth, corresponding to stretching of the aerogel. These samples have been shown to stabilize two new chiral states;\footnote{J. Pollanen et al. Nature Physics, 8, 317-320 (2012).} the higher temperature state being the subject of the present study. Using pulsed NMR we have performed experiments on $^3$He-A imbibed in this sample in two orientations: strain parallel and perpendicular to the applied magnetic field. From the NMR frequency shifts as a function of tip angle and temperature, we find that the angular momentum $\hat{l}$ is oriented along the strain axis, providing evidence for the theory advanced by Sauls. [Preview Abstract] |
Thursday, March 6, 2014 9:24AM - 9:36AM |
S47.00008: Topological mass current on a domain wall in superfluid $^3$He A-phase Yasumasa Tsutsumi At a surface of the superfluid $^3$He A-phase, the surface Andreev bound state accompanied with edge mass current emerges due to a topological phase transition. The topological phase transition also occurs at a domain wall in the A-phase, namely, an interface between the A-phases with the opposite directions of $l$-vector. In the bulk A-phase, the chiral state is characterized by a topological number $\nu=\pm 1$ whose sign depends on the direction of $l$-vector. Topological properties of the Andreev bound state at the domain wall depends on the difference of the topological numbers on each side of the domain wall. I report that the direction and amplitude of the topological mass current parallel to the domain wall depends on, however, not only the difference of the topological numbers but also the difference of phases. Then, we can devise the domain wall without the topological mass current by fixing the appropriate phase difference. I also show the phase dependence of energy loss at the domain wall based on the quasiclassical theory including quasiparticle's information in the Andreev bound state, which is essential for an understanding of the dynamics of the domain walls in the A-phase. [Preview Abstract] |
Thursday, March 6, 2014 9:36AM - 9:48AM |
S47.00009: Superfluid phases of $^{3}$He in a periodic confined geometry Joshua Wiman, J.A. Sauls We report theoretical and computational results on the phases of superfluid $^3$He confined by
a two-dimensional periodic array of square boundaries (``posts'') with maximal
pair-breaking on the boundaries and translational invariance in the third
dimension.
We obtain a phase diagram by numerically minimizing the Ginzburg-Landau free energy functional. Results
are reported for the pressure range $P=0-34\,\mbox{bar}$, based on material parameters that include
strong-coupling corrections that account for the bulk $^3$He phase diagram, and for lattice periods, $L
\le 30\xi_{0}$ and post dimensions, $0.5\xi_{0}\le d < L$.
At all pressures we find a transition from the normal state to a periodic polar phase with
$T_{c1} |
Thursday, March 6, 2014 9:48AM - 10:00AM |
S47.00010: Fermionic spectrum of superfluid phases of $^3$He under strong confinement J.A. Sauls, Hao Wu For superfluid $^3$He in confined geometries and films, the interplay between Fermions confined on opposing surfaces will in general modify the surface spectrum. We calculate the surface spectrum of a polar phase and the B phase confined between specular reflecting on both surfaces. We show that for polar phase the surface bound states will develop a band structure for any in plane momentum with a sub-gap separating the bound states and continuum states. The bandwidth is determined by the thickness of film. However for B-phase, the interplay between surface states does not change the energy spectrum, but only modulates their spectral weight. The wave function of the surface bound states at both surfaces are calculated. It is shown that the bound state energy disperses linearly with parallel momentum $p_{||}$ and even though the spatial part of the wave functions overlap, the Nambu spinors for surface states are orthogonal to each other. This leads to robustness of surface spectrum in highly confined $^3$He-B. We reported that the Nambu spinor at $z = 0$ describes a right-handed helical state, while the Nambu spinor at $z = D$ describes a left-handed helical state. They give rise to a spin currents that are opposite on the opposing surfaces. [Preview Abstract] |
Thursday, March 6, 2014 10:00AM - 10:12AM |
S47.00011: A Quasiparticle Detector for Quantum Turbulence Imaging in Superfluid 3He-B Shaun Fisher, Ian Bradley, Marcel Clovevcko, Sean Ahlstrom, Ed Guise, Rich Haley, Steve Holt, George Pickett, Roch Schanon, Viktor Tsepelin, Andrew Woods We describe the development of a two-dimensional quasiparticle detector to visualise quantum turbulence in superfluid 3He-B at ultra-low temperatures. The detector consists of 25 pixels each containing a miniature quartz tuning fork. The damping on each fork provides a measure of the local quasiparticle flux. The detector is illuminated by a beam of ballistic quasiparticles generated from a near-by black-body radiator. Vortices have a large cross-section for Andreev reflecting ballistic quasiparticles at low temperatures. We generate a tangle of vortices (quantum turbulence) in the path of the beam using a vibrating wire resonator. The vortices cast a shadow onto the face of the detector due to the Andreev reflection. This allows us to image the vortex tangle and to investigate the tangle dynamics. We describe the detector and present some preliminary results. [Preview Abstract] |
Thursday, March 6, 2014 10:12AM - 10:24AM |
S47.00012: Effects of surface roughness on non-uniform phases of superfluid $^3$He and spin-triplet models for Sr$_2$RuO$_4$ Anton Vorontsov, James Sauls We present theoretical and computational results for the spectrum of surface bound states of confined superfluid $^3$He and spin-triplet, odd-parity pairing theories of Sr$_2$RuO$_4$. The surface states, despite being related to the topological structure of the condensed state, are sensitive to surface disorder. We investigate effects of surface roughness on the physical properties of the boundary layer of several coherence lengths. We find that for confined $^3$He-A or chiral phases proposed for Sr$_2$RuO$_4$ the spatial profile of the edge current is significantly modified for atomically rough surfaces compared to that for specular surfaces. The boundary effect is strongly reflected in the ground-state angular momentum generated by the edge states. In thin films of superfluid $^3$He with rough surfaces the effect of surface scattering is expected to be even more important since surface states dominate the thermodynamic properties. For specular boundaries we predicted new phases with spontaneously broken time-reversal or translational symmetries should appear in films of $D \sim 10 \xi_0$. We report results for the phase diagram for specular, diffuse and maximal pair-breaking resulting from retro-reflecting boundaries. [Preview Abstract] |
Thursday, March 6, 2014 10:24AM - 10:36AM |
S47.00013: Phase Diagram for $^3$He Films on Boron Nitride: NMR Studies Yibing Tang, Neil Sullivan Recent studies of the thermodynamic properties of $^3$He films on graphite [1] have revealed the existence of a previously undetected self-bound liquid phase at low density coverages. We report the results of NMR relaxation time studies for $^3$He adsorbed on hexagonal boron nitride designed to explore the dynamics of the adsorbed $^3$He atoms in order to identify the phase boundaries as a function of temperature. A steep thermally activated temperature dependence is observed at high temperatures ($T > 2.6$) K, followed by a linear dependence for $0.77 < T < 2.6$ K. The linear dependence is consistent with that expected for thermal diffusion in the self-bound liquid state.\\[4pt] [1] D. Sato, {\it et al.}, Phys. Rev. Lett. {\bf 109}, 235306 (2012). [Preview Abstract] |
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