Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V06: Correlations in Helium and Hydrogen |
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Sponsoring Units: DCMP Chair: Paul Sokol, Indiana University Bloomington Room: BCEC 109A |
Thursday, March 7, 2019 2:30PM - 2:42PM |
V06.00001: Neutron Scattering Studies of superfluid helium confined in preplated nanoporous materials. Paul Sokol, Garfield Warren, Timothy Prisk, Nathan Nichols, Adrian Del Maestro One dimensional systems have been of long standing interest due to a profound difference from their 2 and 3 dimensional counterparts whose properties can be described in terms of quasi-particles. This quasi-particle picture breaks down completely in one dimension where the fundamental excitations are collective and described by the universal Tomonaga-Luttinger liquid (TLL) theory. Superfluid helium confined in one-dimensional templated materials, such as MCM-41, provide an attractive model system for studying the properties of a TLL. Unfortunately, the pore size attainable in these materials is too large to reach the one-dimensional limit. Preplating these porous materials with an adsorbate offers a route to smaller pore sizes where one-dimensional confinement can occur. We will present the results of neutron scattering studies of the excitations of superfluid helium confined in MCM-41 preplated with a monolayer of Argon. The observed scattering departs dramatically from the bulk superfluid and may be consistent with a TLL. |
Thursday, March 7, 2019 2:42PM - 2:54PM |
V06.00002: The Damping of a Micro-electromechanical Resonator in the Presence of Quantum Turbulence in He II Colin Barquist, Wenguang Jiang, Keegan Gunther, Yoonseok Lee, Ho Bun Chan A micro-electromechanical plate resonator was immersed in 4He down to 13 mK at saturated vapor pressure. The resonator consists of a 125x125x2 μm3 plate suspended 2 μm above a substrate. Due to its small mass and and large surface area it is sensitive to vortices in the fluid and vortices pinned to the surface of the device. The device is studied in the presence of fully developed quantum turbulence generated by a quartz tuning fork and in the presence of remnant vortices pinned to the device. Specifically, the velocity dependent damping of the device in these conditions is measured and reported. |
Thursday, March 7, 2019 2:54PM - 3:06PM |
V06.00003: The Use of 3He in Obtaining Ultra-Low Temperatures at the NHMFL High B/T Facility Andrew Woods, Chao Huan, Naoto Masuhara, Jian-Sheng Xia, Neil Sullivan The High B/T Facility at the National High Magnetic Field Laboratory (NHMFL) provides access to unique ultra-low temperature, high magnetic field and ultra-quiet environments. The facility operates nuclear demagnetization refrigerators capable of reaching 0.5 mK at 16 T and 0.1 mK at 8 T. This enables user experiments in diverse fields including ultrasound studies, FQHE studies in tilted fields, high sensitivity NMR, high sensitivity dielectric measurements, sub-mK susceptibility measurements, novel states (Bose glass, Wigner crystals) and studies of superfluid 3He. These experiments require that the 3He, the electrical leads and samples be efficiently cooled to ultra-low temperatures. In this talk I will discuss the use of liquid 3He in cooling at the High B/T Facility, experimental platforms developed to make best use of this method, recent experimental results obtained, and potential future developments. |
Thursday, March 7, 2019 3:06PM - 3:18PM |
V06.00004: Mass Flux Measurements in Solid 4He. Valentyn Rubanskyi, Robert Hallock We previously explored the characteristics of mass flux through solid 4He that takes place from one superfluid-filled reservoir to the other through a solid-filled experimental cell off the melting curve (1). We measured flow characteristics that appear to match expectations for one-dimensional Luttiinger-Liquid conductivity (2) and we documented the effects that various concentrations of 3He impurity have on the temperature dependence of the flow (3). Our most recent experiments show that reducing the interface between superfluid helium in the Vycor rods and solid helium reduces the flux and that significantly blocking the cross section of the channel filled with solid 4He further suppress the flux. These results further support the possibility that the observed mass flux is be due to the superfluid cores of edge dislocations. |
Thursday, March 7, 2019 3:18PM - 3:30PM |
V06.00005: Dynamics of 1D 3He adsorbed in 4He plated MCM-41: NMR Studies Johnny Adams, Marc L. Lewkowitz, Chao Huan, Naoto Masuhara, Neil S. Sullivan We report the results of NMR studies of the dynamics of 3He confined to 1D in the interior of the hexagonal nanochannels of MCM-41. The walls of the MCM-41 were coated with a monolayer of 4He and 3He was added afterwards to form a 1D 3He line density of 0.1 Å-1. The nuclear spin-lattice relaxation times were measured for temperatures 0.050 < T < 3.0 K. A distinct peak is observed at 95 mK which is interpreted as the expected maximum of the “spin-drag” relaxation time predicted by theory for T = 2TF where TF is the Fermi degeneracy temperature. |
Thursday, March 7, 2019 3:30PM - 3:42PM |
V06.00006: Measuring Corrections to the Amplitude Mode Masses in Superfluid 3He Man Nguyen, Andrew Zimmerman, William Halperin Superfluid 3He has a rich spectrum of collective modes with both massive (gapped) and massless (gapless) excitations. The masses of these modes can be precisely measured with acoustic spectroscopy and fit to theoretical models to extract interaction strengths of the underlying superfluid. Prior comparisons between theory and experiment accounted for Fermi-liquid effects, f-wave interactions, and the strong-coupling energy gap. However, strong-coupling corrections to the mode mass itself were not included. In this work, we employ a simple procedure to incorporate these corrections[1] to the mode which improve the determination of the f-wave pairing strength, (1/x3). Results from several independent experiments are brought into better agreement with the improved theoretical model. |
Thursday, March 7, 2019 3:42PM - 3:54PM |
V06.00007: The Polar Phase of Superfluid 3He in the Limit of Small Anisotropy Andrew Zimmerman, Man Nguyen, William Halperin The polar phase of superfluid 3He is characterized by a single orbital component of the p-wave order parameter, and is favored by the breaking of the orbital rotational symmetry. This can be achieved by introducing anisotropic impurities into pure superfluid. This method has been used experimentally to stabilize the polar phase in the limit of extremely large impurity anisotropy produced by aligned Al2O3 strands.1 However, it has been predicted that even small anisotropy is enough to break the rotational symmetry and stabilize the polar phase close to the transition temperature.2 Here, we report evidence for the polar phase in the limit of small impurity anisotropy. We produce this anisotropic impurity by compressing 98% porous silica aerogel by ~20%. At low pressure, P < 7.5 bar, we observe a change in the behavior of the NMR spectra in the superfluid. The high temperature phase at these pressures has a larger NMR frequency shift than the A-phase, while remaining an equal spin pairing state. This is consistent with the polar phase being the equilibrium state near Tc at low pressure. |
Thursday, March 7, 2019 3:54PM - 4:06PM |
V06.00008: Simplified calculations of the frequencies of Higgs modes in superfluid 3He-B using N-point Padé approximants John Paliotta, Joseph W Serene Previous calculations of the frequencies of the Higgs modes in superfluid 3He-B have been done on the real-frequency axis, most recently using the Keldysh formalism. Recently Sauls and Mizushima[1] showed how the unperturbed weak-coupling mode frequencies can be found by solving the imaginary-frequency version of the kinetic equation, followed by standard analytic continuation to real frequencies and evaluation of remaining integrals there. We show that perturbed frequencies due to magnetic fields or strong-coupling effects can be calculated on the imaginary axis and the final results can then be obtained, to high accuracy, by N-point Padé approximants, which greatly simplifies these calculations. [1] J.A. Sauls and Takeshi Mizushima, On the Nambu fermion-boson relations for superfluid 3He, Phys. Rev. B 95, 094515 (2017) |
Thursday, March 7, 2019 4:06PM - 4:18PM |
V06.00009: Quantum Monte Carlo simulation of superfluid helium confined inside pre-plated nanoporous materials Nathan Nichols, Adrian Del Maestro, Timothy Prisk, Garfield Warren, Paul Sokol In one spatial dimension, enhanced thermal and quantum fluctuations should preclude the existence of any long range ordered superfluid phase of matter. Mesoporous ordered silica-based structures such as the molecular sieve MCM-41 offer an experimental route towards the observation of this effect through the physical confinement of superfluid helium inside quasi-one-dimensional channels. However, the angstrom-scale coherence length of the wavefunction away from the bulk superfluid transition temperature requires novel nano-engineering approaches to reach the one-dimensional limit. In this talk we will describe ab initio quantum Monte Carlo simulations of superfluid helium confined inside MCM-41 that has been pre-plated with adsorbates to reduce the diameter of the confining media. We will describe how the choice of adsorbate (e.g. argon, neon, krypton) can be modified to obtain different types of helium structures inside the pores. Phase and density correlations may be further tuned via the external pressure of helium with the goal of realizing an emergent one-dimensional quantum liquid. |
Thursday, March 7, 2019 4:18PM - 4:30PM |
V06.00010: Anomalous attenuation of piezoacoustic surface waves by liquid helium thin films Kostyantyn Nasyedkin, Heejun Byeon, Justin Lane, Liangji Zhang, Niyaz Beysengulov, Reza Loloee, Johannes Pollanen We report on the experimental observation of an anomalously high attenuation of high frequency surface acoustic waves (SAW) by thin films of liquid 4He [1]. The piezoelectric SAW propagate along the surface of a lithium niobate substrate, which is covered by liquid helium films of varying thicknesses. When the thickness of the helium layer is much larger than the wavelength of the SAW on the substrate the SAW attenuation is dominated by emitting compressional waves into the bulk liquid, in good agreement with theory and previous measurements. However, for sufficiently thin helium films, we find that the SAW attenuation significantly exceeds that measured with the substrate submerged in bulk liquid. Possible mechanisms for this enhanced attenuation are discussed. |
Thursday, March 7, 2019 4:30PM - 4:42PM |
V06.00011: Elastic Anomaly of Helium, Hydrogen and Neon Films on Disordered Substrate Takahiko Makiuchi, Katsuyuki Yamashita, Michihiro Tagai, Yusuke Nago, Keiya Shirahama We report systematic elasticity measurements of helium (4He and 3He), hydrogen (H2, HD, D2) and neon films physisorbed on a porous glass substrate. The elastic constant and dissipation as a function of temperature were measured by means of torsional oscillator technique with changing the film coverage. We have found that films of all species (4He, 3He, H2, HD, D2, Ne) showed an increase of the elastic constant accompanied by a dissipation peak at low temperatures, which we call the elastic anomaly. This suggests that any atomic and molecular films adsorbed on disordered substrates exhibit a crossover from a soft state at high temperature to a stiff state at low temperature. Only 4He and 3He films exhibit insulator–(super)fluid quantum phase transitions at critical coverages corresponding to about 2 atomic layers. Helium films below those critical coverages are in a gapped and compressible ground state. Hydrogen films show multiple dissipation peaks depending on the film coverage. The elastic anomaly of neon has single dissipation peak, and the peak temperature did not decrease below 5 K which signifies quantum phase transition does not occur in neon films. |
Thursday, March 7, 2019 4:42PM - 4:54PM |
V06.00012: Transition in Wave Behavior on a Superfluid Vortex at Large Excitation Amplitude Rena Zieve, Josephine Spiegelberg, Andrew Diggs We study a single quantized vortex stretched between a wire and the wall of a cylindrical container. The wire serves both as a probe and as a means of exciting the system. Vibrating the wire creates oscillations along the vortex. One consequence of these oscillations is that the spot where the vortex joins the wire moves. This in turn changes the normal modes of the wire's vibration, which lets us detect the vortex location. We find a qualitative change in behavior at sufficiently large excitation. Below the crossover, clear vortex waves are induced, with amplitude near the expected threshold for instability. As the excitation increases, the signal becomes much less regular. Higher-frequency oscillations appear, as well as a slow feature that may indicate recurrence. The vortex appears to undergo significant length changes during the process. |
Thursday, March 7, 2019 4:54PM - 5:06PM |
V06.00013: Molecular mean-squared displacement in solid parahydrogen Timothy Prisk, Douglas L Abernathy, Garrett E Granroth, Scott Hanna, Todd Sherline, Richard Azuah The condensed phases of molecular hydrogen are systems of fundamental importance in quantum many-body physics. Zero-point motion makes a large contribution to the kinetic energy and mean-squared displacement <u2> of hydrogen molecules in the liquid and solid phases. At present, there is a significant disagreement between theory and experiment about the relative importance of thermal and quantum effects near the liquid-solid phase transition of parahydrogen. Path Integral Monte Carlo calculations predict that <u2> increases as the melting temperature is approached from below, implying a combination of thermal and quantum effects [Phys. Rev. B 95, 104518 (2017)]. However, an inelastic neutron scattering study of the rotational transitions in solid parahydrogen suggests that <u2> is independent of temperature, and is thus determined by quantum-mechanical zero-point motion alone [Phys. Rev B 86, 144524 (2012)]. In this presentation, we report new inelastic neutron scattering measurements of <u2> obtained using the ARCS spectrometer at Oak Ridge National Laboratory and the DCS spectrometer at the NIST Center for Neutron Research. |
Thursday, March 7, 2019 5:06PM - 5:18PM |
V06.00014: Heat Capacity Studies of Nanoconfined Hydrogen Erin Marlowe, Paul Sokol The effect of confinement on the thermodynamic properties and phase transitions of liquids and solids in confinement has been of long-standing interest and recent interest has focused on the effects of dimensionality. Hydrogen has been of interest due to the importance of quantum effects, in particular zero-point motion, and has been studied extensively in a variety of porous media. Templated porous materials, such as MCM-41, provide an attractive model system for studying the effects of confinement due to their highly uniform one-dimensional pores with variable pore size. Unfortunately, the minimum pore diameter is typically limited to a few nanometers which limits our ability to approach the one-dimensional limit. We will present measurements of adsorption isotherms and heat capacity of hydrogen confined in MCM-41. We will present the results for both bare MCM-41 and samples that have been preplated with noble gases to reduce the effective pore diameter |
Thursday, March 7, 2019 5:18PM - 5:30PM |
V06.00015: Higher-order quantum hydrodynamics for supersolids Vili Heinonen, Keaton Burns, Jorn Dunkel Supersolids are theoretically predicted quantum states that break the continuous rotational and translational symmetries of liquids while preserving superfluid transport properties. |
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