Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session S63: Helium and Exotic SuperfluidsRecordings Available
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Sponsoring Units: DCMP Chair: Adrian Del Maestro, University of Tennessee Room: Hyatt Regency Hotel -Grant Park A |
Thursday, March 17, 2022 8:00AM - 8:12AM |
S63.00001: 3He Dynamics in Quasi-1D Below the Fermi Degeneracy Temperature Johnny L Adams, Marc L Lewkowitz, Chao Huan, Donald Candela, Neil S Sullivan, Naoto Masuhara We use NMR techniques to study the spin dynamics of 3He in quasi-1D confinement for temperatures well below the Fermi degeneracy temperature TF. The quasi-1D channel was provided by MCM-41 mixed with ultra-fine silver powder and plated with a monolayer of 4He. The spin dynamics were measured using both low power pulsed and continuous wave NMR experiments. We explore the nuclear spin-lattice relaxation for temperatures 10 < T < 500mK. We observe one of the hallmarks of Luttinger liquid physics, a linear temperature dependence of the relaxation dynamic at very low temperatures, T < TF. For T > TF, the effect of transverse excitations reduced the relaxation times below the predicted T-1/2 dependence for a one-dimensional Fermi system. |
Thursday, March 17, 2022 8:12AM - 8:24AM |
S63.00002: New Phases and Angular Momentum of Rotating Chiral p-Wave Superfluids Confined in an Annulus Jason He, James A Sauls Persistent mass currents of a chiral p-wave superfluid confined in a toroidal annulus stabilize new equilibrium states. We present theoretical calculations of the corresponding phase diagram, the internal structure of the superfluid order parameter, and the angular momentum based on the Ginzburg-Landau free energy functional for 3He. For sufficiently small persistent current the angular momentum of the chiral phase is quantized in integer units given by the winding number of the global phase. These low-flow states can be stabilized by rotating the annulus at certain critical angular velocities. As the winding number is increased an asymmetry between the edge currents on the inner and outer radius develops, and at the critical value of the persistent current the superfluid undergoes a transition to a spatially inhomogeneous axial domain wall phase. We show that this phase is energetically favored at sufficiently large persistent current, with both the edge and domain wall currents counter-propagating relative to the bulk supercurrent. The axial domain wall state is also metastable down to zero bulk flow and exhibits a significantly increased angular momentum compared with the stable chiral ground state. This anomaly in the angular momentum is a direct signature of the axial domain wall phase of the superfluid condensate. |
Thursday, March 17, 2022 8:24AM - 8:36AM |
S63.00003: Incipient Pair-Fluctuation Corrections to Quasiparticle Transport in Liquid 3He Wei-Ting Lin, James A Sauls Nonequilibrium properties of a Fermi liquid are well described by a Boltzmann-Landau kinetic equation for the quasiparticle distribution function. For such a system at temperatures near the superfluid/superconductor phase transition, Cooper pair fluctuations are long-lived and can influence physical properties of the normal phase. We report new results for the leading corrections to the Landau kinetic equation using the Keldysh method that result from quasiparticle emission and absorption of long-lived pair fluctuations. As an application of our theory we calculate the increase in the attenuation of zero sound attenuation that results from the scattering of quasiparticles by long-lived pair fluctuations. The theoretical results are in excellent agreement with both the temperature and pressure dependence of the excess attenuation of zero sound reported by Paulson and Wheatley [1]. We also predict a correction to the zero sound velocity which should be observable. |
Thursday, March 17, 2022 8:36AM - 8:48AM |
S63.00004: The Orbital Analog of the Spin-Flop Transition in Superfluid 3He and the Structure of Anisotropic Aerogel Man D Nguyen, Joshua Simon, John W Scott, William P Halperin Recently, sharp transitions were observed in superfluid 3He imbibed in anisotropic silica aerogel that are analogous to the spin-flop transition seen in antiferromagnets. The Cooper pair orbital angular momentum in both the A- and B-phases spontaneously reorients by 90o uniformly across the entire system as temperature or pressure is swept1,2,3. We propose that the anisotropic structure present in the aerogel is the driving mechanism for this transition. To better characterize these aerogels, we perform diffusion-limited cluster aggregation simulations. By biasing the diffusion process, we obtained two distinct classes of globally, anisotropic aerogels which we call "nematic" and "planar". The calculated structure factor from simulated aerogels is compared with small-angle X-ray scattering of lab-grown aerogels allowing us to classify the spatial structure of the lab-grown samples. Unexpectedly, lab-grown compressed aerogel has nematic structure while lab-grown stretched aerogel has planar structure. This surprising classification however produces a consistent model for the reorientation of the orbital angular momentum. |
Thursday, March 17, 2022 8:48AM - 9:00AM |
S63.00005: Helium Physics Using HeRALD: The Helium Roton Apparatus for Light Dark Matter Doug Pinckney The HeRALD experiment uses sub-100 mK superfluid 4He to study particle interactions, in particular, dark matter-nucleon scattering. The detector uses singlet and triplet electronic excitations, and quantum evaporation from vibrational quasiparticles to determine the energy and nature of the particle interaction. In this talk I will present progress towards the observation of the quantum evaporation signal using a next generation athermal phonon detector. I will also discuss the broader R&D program, with an emphasis on the helium and materials physics we will study to refine the detector. |
Thursday, March 17, 2022 9:00AM - 9:12AM |
S63.00006: Superfluid Helium-3 in Aerogel in the Absence of Magnetic Scattering John W Scott, Man D Nguyen, William P Halperin Confining superfluid helium-3 in a porous aerogel both suppresses and alters the relative stabilities of the superfluid. Moreover, the presence of disorder and anisotropy in the imbibed superfluid helium-3 system can work to alter the orientation of the order parameter, supporting well-resolved order parameter orientation transitions and superfluid glass phases[1,2]. We report results of ongoing pulsed NMR studies over a range of fields 0.05T-0.2T of superfluid helium-3 imbibed in isotropic and both 7% and 12% radially shrunken aerogels, with magnetic impurity scattering channels suppressed by a coating of solid helium-4 on the surface of the aerogel[3]. Prior experiments in radially shrunken aerogels observed the total suppression of non-equal spin pairing phases of helium-3 and, likewise, previous experiments in homogeneous aerogels have exhibited superfluid glass phases of helium-3, with both 2-dimensional and 3-dimensional disordered phases observed depending on the phase from which the superfluid glass is nucleated[4,1]. |
Thursday, March 17, 2022 9:12AM - 9:24AM |
S63.00007: Study of the structure of helium films in nanoengineered pores. Paul E Sokol, Garfield T Warren, Timothy R Prisk Ordered templated porous materials such as MCM-41 offer an attractive platform for studying the effects of reduced dimensionality. Unfortunately, the attainable minimum pore diameters in these materials are still too large to reach the one-dimensional limit for helium. Recently Nichols et al have suggested that preplating MCM-41 pores with a rare gas can effectively reduce the effective pore diameter and modify the helium-pore interactions sufficiently to allow one-dimensional behavior to be observed. We have carried out small angle neutron scattering (SANS) studies of the adsorption of helium in argon preplated pores of MCM-41. Templated ordered materials such as MCM-41 have an ordered array of 1D pores and SANS yields a series of diffraction peaks determined by the inter-pore spacing. The intensity of these diffraction peaks yields information on the radial density within the pores. We will present results for the growth of argon layers and for the growth of helium in pores preplated with a monolayer of helium |
Thursday, March 17, 2022 9:24AM - 9:36AM |
S63.00008: Tracking normal fluid flow in He II with unsupervised machine learning Xin Wen, Landen McDonald, Josh Pierce, Wei Guo, Michael Fitzsimmons Time dependent observations of fluid flow around large objects in three dimensions under extreme conditions are necessary to measure point-to-point correlations of the velocity vector field (structure functions) resulting from flow perturbed by objects. Using thermal gradients, we induced flow of the normal fluid component of liquid He II and observed the flow by recording fluorescence of excimers produced by neutron capture throughout a ~cm3 volume. We applied an unsupervised machine learning algorithm to identify individual excimer clouds and then track their motion with millimeter and millisecond precision. Owing to the fact excimers are produced over a large region, the data are sparse in comparison to other techniques to produce excimers. Machine learning is crucially important to track flow represented by sparse data and its importance will increase as improvements are made to overcome the sparsity of data. |
Thursday, March 17, 2022 9:36AM - 9:48AM |
S63.00009: Experimental Realization of One Dimensional Helium Paul E Sokol, Adrian G Del Maestro, Nathan S Nichols, Garfield T Warren, Timothy R Prisk Spatial dimension is key to the ordered behaviors a system can exhibit. As the dimension is lowered, locally stabilizing interactions are reduced, leading to the emergence of phases of matter without purely classical analogues, e.g. spin liquids, Dirac fermions and the fractional quantum Hall effect in two-dimensions (2D). Realizing 1D platforms has been elusive, due to their inherent lack of stability, with a few notable exceptions such as spin chains and ultracold low-density gasses. The inability of such systems to exhibit long range order is essential to their universal description in terms of the Tomonaga-Luttinger liquid theory. Here we describe experimental observation and theoretical studies of this behavior using a nanoengineering approach that preplates a templated material with 1D cyclindrical pores (MCM-41) with a noble gas to reduce the spatial dimension. The resulting excitations of the confined 4He, confirmed by neutron scattering, are qualitatively different than three and two-dimensional superfluid helium, and consistent with Quantum Monte Carlo calculations. The results can be analyzed in terms of a mobile impurity in an otherwise linear Luttinger liquid allowing for the extraction of the microscopic parameters describing the emergent quantum liquid. |
Thursday, March 17, 2022 9:48AM - 10:00AM |
S63.00010: Coulomb-gas sum rules for vortex-pair fluctuations in 2D superfluids Karla Galdamez, Gary A Williams, Mingyu Fan, Charlie McDowell Coulomb-gas sum rules are used to characterize thermal vortex-pair fluctuations in 2D superfluids. Simulations of the 2D XY model have been carried out to study the net winding number of vortices at a given temperature in a circle of radius R, squared and averaged over 1000 instances. At all temperatures the net squared winding number is found to scale as a perimeter law, linear in R, in agreement with Coulomb-gas theories [1], and at infinite temperature agrees nearly exactly with an early theory by D. Dhar [2]. The linear slope of the perimeter variation is found to display a sharp peak with temperature, starting below the critical Kosterlitz-Thouless temperature TKT and peaking near 1.15 TKT, very similar to the peak in specific heat. We have also computed the vortex-vortex distribution functions, finding an asymptotic power-law variation in the vortex separation distance at all temperatures. In conjunction with a Coulomb-gas sum rule [1] on the perimeter fluctuations, these can be used to successfully model the start of the perimeter-slope peak in the region below TKT. |
Thursday, March 17, 2022 10:00AM - 10:12AM |
S63.00011: A finite-momentum superfluid on a frustrated honeycomb lattice Tzu-Chi Hsieh, Han Ma, Leo R Radzihovsky We study finite-momentum superfluidity in a frustrated honeycomb Bose-Hubbard model that exhibits a dispersion minimum on a closed curve - a "moat". Boson condensation on any point of the moat minimum leads to a novel smectic superfluid state with fluctuations qualitatively stronger than in conventional superfluids. We compute a variety of its properties, including condensate depletion, equation of state, momentum distribution, and structure function. While stable at zero temperature, in a continuum approximation such superfluid exhibits a 3d quasi-long-range order at any nonzero temperature. Quantum order-by-disorder at low energies manifests lattice-broken rotational symmetry and asymptotically leads to a crossover to a conventional long-range ordered superfluid state. We complement the microscopic lattice analysis with a field theory description for such nonzero momentum superfluids, finding a reassuring agreement and allowing us to confront general questions about such phenomena. |
Thursday, March 17, 2022 10:12AM - 10:24AM |
S63.00012: Development of the electrohydrodynamic instability of charged liquid helium surface Pranaya K Rath, Ambarish Ghosh Electrons on the surface of liquid helium behave as an ideal 2-dimensional electron system (2DES), whereas helium surface can't bear more than a certain critical electron density. Once the critical electron density is reached, the helium surface becomes unstable which ultimately results in the formation of MEBs. in this work, we present experimental observations of the dynamics of the instability and its temporal dependence on the surface electron density. Image analysis based on Fast Fourier Transforms was used to determine the unstable wave vectors from the acquired images, which was found to agree well with the theoretical formulae. |
Thursday, March 17, 2022 10:24AM - 10:36AM |
S63.00013: Landau instability of strongly-coupled superfluids from hydrodynamics Blaise Gouteraux, Eric Mefford, Filippo Sottovia Hydrodynamics provides an effective description of superfluids at scales large compared to the local equilibration scales. It is well-known that superfluids become unstable when a sufficiently large superfluid velocity is turned on. In this talk, I will explain how this instability can be captured within hydrodynamics, giving a simple expression for the critical velocity in terms of thermodynamic data. I will demonstrate that this is the mechanism responsible for the Landau instability in strongly-coupled superfluids constructed using Gauge/Gravity duality. This is in contrast to Helium 4 where rotons are responsible for the instability. |
Thursday, March 17, 2022 10:36AM - 10:48AM |
S63.00014: Triangular Pair-Density Wave in Confined Superfluid 3He Pramodh V Senarath Yapa Arachchige, Rufus Boyack, Joseph Maciejko Recent advances in experiment and theory suggest that superfluid 3He under planar confinement may form a pair-density wave (PDW) whereby superfluid and crystalline orders coexist. While a natural candidate for this phase is a unidirectional stripe phase predicted by Vorontsov and Sauls in 2007, recent nuclear magnetic resonance measurements of the superfluid order parameter rather suggest a two-dimensional PDW with noncollinear wavevectors, of possibly square or hexagonal symmetry. In this work, we present a general mechanism by which a PDW with the symmetry of a triangular lattice can be stabilized, based on a superfluid generalization of Landau's theory of the liquid-solid transition. A soft-mode instability at finite wavevector within the translationally invariant planar-distorted B phase triggers a transition from uniform superfluid to PDW that is first order due to a cubic term generally present in the PDW free-energy functional. This cubic term also lifts the degeneracy of possible PDW states in favor of those for which wavevectors add to zero in triangles, which in two dimensions uniquely selects the triangular lattice. |
Thursday, March 17, 2022 10:48AM - 11:00AM |
S63.00015: Thermal Hall Transport in Confined Superfluid 3He Priya Sharma, James A Sauls, Anton Vorontsov NMR experiments on liquid 3He infused into uniaxially anisotropic silica aerogels show the stabilisation of two equal-spin-pairing (ESP) chiral phases on cooling from the normal phase. The alignment of the chiral axis relative to the anisotropy axis for these phases is predicted to depend upon temperature. A chiral A-like phase is also stabilized when 3He is confined to a slab of thickness D ≈ ξ, the superfluid coherence length. For both types of confinement, scattering of quasiparticles by the random potential - aerogel or surface - is pair breaking and generates a sub-gap density of quasiparticle states (DOS). The random field also conspires with the chiral order parameter to generate skew scattering of quasiparticles in the plane normal to the chiral axis. This scattering mechanism leads to anomalous thermal Hall transport for nonequilibrium quasiparticles driven by a thermal gradient. We report theoretical results for the anomalous thermal Hall conductivity for theoretical models for chiral phases of 3He in both anisotropic aerogel and slabs, including the proposed biaxial chiral phase. |
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