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: ^{3}He Dynamics in Quasi1D 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 ^{3}He in quasi1D confinement for temperatures well below the Fermi degeneracy temperature T_{F}. The quasi1D channel was provided by MCM41 mixed with ultrafine silver powder and plated with a monolayer of ^{4}He. The spin dynamics were measured using both low power pulsed and continuous wave NMR experiments. We explore the nuclear spinlattice 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 < T_{F}. For T > T_{F}, the effect of transverse excitations reduced the relaxation times below the predicted T^{1/2} dependence for a onedimensional Fermi system. 
Thursday, March 17, 2022 8:12AM  8:24AM 
S63.00002: New Phases and Angular Momentum of Rotating Chiral pWave Superfluids Confined in an Annulus Jason He, James A Sauls Persistent mass currents of a chiral pwave 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 GinzburgLandau free energy functional for ^{3}He. 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 lowflow 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 counterpropagating 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 PairFluctuation Corrections to Quasiparticle Transport in Liquid ^{3}He WeiTing Lin, James A Sauls Nonequilibrium properties of a Fermi liquid are well described by a BoltzmannLandau kinetic equation for the quasiparticle distribution function. For such a system at temperatures near the superfluid/superconductor phase transition, Cooper pair fluctuations are longlived 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 longlived 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 longlived 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 SpinFlop Transition in Superfluid ^{3}He and the Structure of Anisotropic Aerogel Man D Nguyen, Joshua Simon, John W Scott, William P Halperin Recently, sharp transitions were observed in superfluid ^{3}He imbibed in anisotropic silica aerogel that are analogous to the spinflop transition seen in antiferromagnets. The Cooper pair orbital angular momentum in both the A and Bphases spontaneously reorients by 90^{o} uniformly across the entire system as temperature or pressure is swept^{1,2,3}. We propose that the anisotropic structure present in the aerogel is the driving mechanism for this transition. To better characterize these aerogels, we perform diffusionlimited 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 smallangle Xray scattering of labgrown aerogels allowing us to classify the spatial structure of the labgrown samples. Unexpectedly, labgrown compressed aerogel has nematic structure while labgrown 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 sub100 mK superfluid 4He to study particle interactions, in particular, dark matternucleon 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 Helium3 in Aerogel in the Absence of Magnetic Scattering John W Scott, Man D Nguyen, William P Halperin Confining superfluid helium3 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 helium3 system can work to alter the orientation of the order parameter, supporting wellresolved order parameter orientation transitions and superfluid glass phases[1,2]. We report results of ongoing pulsed NMR studies over a range of fields 0.05T0.2T of superfluid helium3 imbibed in isotropic and both 7% and 12% radially shrunken aerogels, with magnetic impurity scattering channels suppressed by a coating of solid helium4 on the surface of the aerogel[3]. Prior experiments in radially shrunken aerogels observed the total suppression of nonequal spin pairing phases of helium3 and, likewise, previous experiments in homogeneous aerogels have exhibited superfluid glass phases of helium3, with both 2dimensional and 3dimensional 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 MCM41 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 onedimensional limit for helium. Recently Nichols et al have suggested that preplating MCM41 pores with a rare gas can effectively reduce the effective pore diameter and modify the heliumpore interactions sufficiently to allow onedimensional behavior to be observed. We have carried out small angle neutron scattering (SANS) studies of the adsorption of helium in argon preplated pores of MCM41. Templated ordered materials such as MCM41 have an ordered array of 1D pores and SANS yields a series of diffraction peaks determined by the interpore 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 pointtopoint 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 ~cm^{3} 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 twodimensions (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 lowdensity gasses. The inability of such systems to exhibit long range order is essential to their universal description in terms of the TomonagaLuttinger 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 (MCM41) 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 twodimensional 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: Coulombgas sum rules for vortexpair fluctuations in 2D superfluids Karla Galdamez, Gary A Williams, Mingyu Fan, Charlie McDowell Coulombgas sum rules are used to characterize thermal vortexpair 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 Coulombgas 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 KosterlitzThouless temperature T_{KT} and peaking near 1.15 T_{KT}, very similar to the peak in specific heat. We have also computed the vortexvortex distribution functions, finding an asymptotic powerlaw variation in the vortex separation distance at all temperatures. In conjunction with a Coulombgas sum rule [1] on the perimeter fluctuations, these can be used to successfully model the start of the perimeterslope peak in the region below T_{KT}. 
Thursday, March 17, 2022 10:00AM  10:12AM 
S63.00011: A finitemomentum superfluid on a frustrated honeycomb lattice TzuChi Hsieh, Han Ma, Leo R Radzihovsky We study finitemomentum superfluidity in a frustrated honeycomb BoseHubbard 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 quasilongrange order at any nonzero temperature. Quantum orderbydisorder at low energies manifests latticebroken rotational symmetry and asymptotically leads to a crossover to a conventional longrange 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 2dimensional 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 stronglycoupled 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 wellknown 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 stronglycoupled 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 PairDensity Wave in Confined Superfluid ^{3}He Pramodh V Senarath Yapa Arachchige, Rufus Boyack, Joseph Maciejko Recent advances in experiment and theory suggest that superfluid ^{3}He under planar confinement may form a pairdensity 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 twodimensional 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 liquidsolid transition. A softmode instability at finite wavevector within the translationally invariant planardistorted B phase triggers a transition from uniform superfluid to PDW that is first order due to a cubic term generally present in the PDW freeenergy 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 ^{3}He Priya Sharma, James A Sauls, Anton Vorontsov NMR experiments on liquid ^{3}He infused into uniaxially anisotropic silica aerogels show the stabilisation of two equalspinpairing (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 Alike phase is also stabilized when ^{3}He 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 subgap 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 ^{3}He in both anisotropic aerogel and slabs, including the proposed biaxial chiral phase. 
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