Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session E20: Superfluid Helium: Experiment |
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Sponsoring Units: DCMP Chair: Joe Serene, Georgetown University Room: 280 |
Tuesday, March 14, 2017 8:00AM - 8:12AM |
E20.00001: Pinning and Melting of a Quantum Wigner Crystal Talbot Knighton, Alessandro Serafin, Zhe Wu, Vinicio Tarquini, Jian-Sheng Xia, Neil Sullivan, Jian Huang, Loren Pfeiffer, Ken West Quantum Wigner crystals (WC) are a remarkable interaction-driven phase that is expected to display manybody pinning in arbitrarily low disorder. For two-dimensional (2D) systems, application of a perpendicular magnetic field quenches the kinetic energy and so that the reentrant and high field insulating phases are considered strong candidates for WC. However, there are large discrepancies in the pinning threshold and lacking evidence of melting since only activated transport has been found. Here we demonstrate strongly non-linear transport for high mobility ($\mu = 3.0 \times 10^6$ cm$^2$/Vs) dilute 2D holes ($p=4.5\times10^{10}$ cm$^{-2}$) at the reentrant phase near filling factor $\nu = 1/3$ in a 20nm GaAs/AlGaAs/GaAs square well. A striking threshold appears below 30 mK at the center of this peak where the holes are pinned within a narrow range of 5pA with equivalent resistance greater than 1 G$\Omega$. This breaks down at larger currents where the differential resistance plummets by more than 3 orders of magnitude. Heating also destroys the threshold while resistance drops in a non-activated fashion. This demonstrates the existence of a pinned WC that appears to undergo a second-order transition upon heating, in agreement with previous theoretical studies. [Preview Abstract] |
Tuesday, March 14, 2017 8:12AM - 8:24AM |
E20.00002: The dynamic critical exponent $y$ for superfluid helium near absolute zero Vladimir Udodov We propose a new interpolation formula for the dynamic critical exponent $y$ for the mixture of liquid He$^{4}$ and He$^{3}$ at low temperatures: \begin{equation} \label{eq1} y=(1+S_{I} -\alpha )\left( {\frac{1}{d}+\frac{1}{6}} \right)\,\,\,\,, \end{equation} where $d$ is the space dimension. In the case of $d=$3, it takes the form \[ y=z\nu =\frac{3\nu }{2}=\frac{1+S_{I} -\alpha }{2}\,(\,T_{C} \ge 0,\,\,\alpha <0)\,,\,(2) \] where \begin{equation} \label{eq2} S_{I} =\left( {\frac{T_{C} }{T }} \right)^{n},\,\,T>T_{C} =T_{\lambda } \,\,, \end{equation} $n$ is some positive constant [1], $z$ is the dynamic critical exponent and $\nu $ is the critical exponent of the correlation length. New formulas~apply not only to positive~critical temperatures $Ò_{Ñ}$ but also ~to the limiting~case~$T_{C}\to $0, which ~realizes in a mixture of~liquid~helium isotopes. The results can be applied to the systems with multi-component order parameter, when the thermodynamic potential depends on the sum of the squares of the components. Examples include Heisenberg ferromagnets and systems undergoing quantum phase transitions. 1.\textit{ Udodov V.N.} New consequences of the static scaling hypothesis at low temperatures. \underline {Physics of the Solid State}. 2015. Ò. 57. \underline {¹ 10}. Ñ. 2073-2077. DOI: \underline {10.1134/S1063783415100340}. [Preview Abstract] |
Tuesday, March 14, 2017 8:24AM - 8:36AM |
E20.00003: Superfluid $^4$He phases on strained graphene Nathan Nichols, Valeri Kotov, Adrian Del Maestro We have investigated the low temperature phases of $^4$He adsorbed on a suspended graphene sheet under uniaxial strain via large scale quantum Monte Carlo simulations. The mechanical deformation of the substrate can modify the induced dipolar (van der Waals) interactions between helium atoms and the surface. The resulting potential can be tuned to exhibit significant spatial anisotropy which is reflected in the commensurate structure of the first adsorbed layer of helium. As the chemical potential is increased, a second layer is adsorbed, and we observe signatures of anisotropic superfluidity with enhanced flow in the zigzag direction. We discuss implications for the experimental observation of this novel two dimensional quantum liquid. [Preview Abstract] |
Tuesday, March 14, 2017 8:36AM - 8:48AM |
E20.00004: Dislocation Structure and Mobility in hcp $^4$He Maurice de Koning, Edgar Josué Landinez Borda, Wei Cai By means of Path Integral Monte Carlo Simulations, we assess the core structure and mobility of screw and edge basal-plane dislocations in hcp $^4$He [1]. The results provide insight into the giant plasticity phenomenology, and show that the cores of both types of dislocation dissociate into non-superfluid Shockley partials separated by a stacking fault. Moreover, the displacement of the centroid positions of the partial cores exhibits considerable fluctuations even in absence of applied shear stresses. This is an indication of negligible lattice resistance to the dislocation motion, in accordance with the experimental observation of giant plasticity. Further results point out that aside from the dislocation structure, zero-point fluctuations play a role in this negligible lattice resistance. [1] Edgar Josué Landinez Borda, Wei Cai, and Maurice de Koning, Phys. Rev. Lett. 117, 045301 (2016). [Preview Abstract] |
Tuesday, March 14, 2017 8:48AM - 9:00AM |
E20.00005: Probing the $^3$He distribution in coexisting liquid and solid $^4$He Zhigang Cheng, John Beamish Substantial attention has been focused on recent experiments of $^4$He mass flow across solid-liquid interfaces and within completely solid samples. The flow is suppressed by $^3$He impurities and appears to involve superfluid pathways: microscopically thin superfluid layers, dislocations with superfluid cores allowing superclimb, or both. It is clear that $^3$He accumulates in the liquid $^4$He and on solid-liquid interfaces, depleting the $^3$He concentration in the solid at low temperature. Here we report a preliminary study of the $^3$He concentration in the liquid phase of solid-liquid coexisting samples. By measuring the capacitance between two concentric cylinders immersed in the liquid helium, we are able to detect movement of $^3$He between the solid and liquid phases, thanks to the dependence of the dielectric constant on $^3$He concentration. We measure the migration of $^3$He into the liquid at low temperatures and find that the time constant for the concentrations to equilibrate is longer at lower temperature. [Preview Abstract] |
Tuesday, March 14, 2017 9:00AM - 9:12AM |
E20.00006: Superfluid Mass Decoupling in Two-dimensional $^{\mathrm{4}}$He: a Double-frequency TO Study Jaewon Choi, Oleksiy Zadorozhko, Eunseong Kim Helium film adsorbed on graphite substrates has been investigated as a realization of quasi-two-dimensional system. Interplay of interactions between helium atoms and substrate offer a rich phase diagram. Especially, Crowell and Reppy reported an anomalous superfluid signal in the second layer of $^{\mathrm{4}}$He films adsorbed on Grafoam from their torsional oscillator (TO) experiment. This signal, reproduced successfully by recent measurements, suggests the possibility of supersolid phase in which both crystalline and superfluid orders coexist. However, an ab initio Monte Carlo calculation did not agree with supersolid interpretation: no commensurate solid phase in the corresponding range of atomic density (or coverage). In this study, we investigated superfluid mass decoupling in the second layer of $^{\mathrm{4}}$He film adsorbed on Grafoil at two different resonant frequency. A double-frequency TO was employed to study the frequency dependence of the TO responses to identify whether the response can be attributed to the appearance of superfluid or not. Both period shift and dissipation were measured in the atomic coverages ranging from 17 to 20 atoms/nm$^{\mathrm{2}}$ where the superfluid responses were reported. A diaphragm-type capacitive strain gauge was also mounted above the sample cell for in-situ pressure measurement. [Preview Abstract] |
Tuesday, March 14, 2017 9:12AM - 9:24AM |
E20.00007: Mass transport though 8 $\mu $m thick solid helium samples without dislocation intersections Jae ho Shin, Duk Young Kim, Ariel Haziot, Moses H.W. Chan We have measured mass flow induced by fountain effect through 8 $\mu $m thick solid helium samples sandwiched between Vycor rods infused with superfluid. Since the network length of dislocation is on the order of the thickness of our sample, we expect the dislocation lines in the sample will be pinned at the Vycor surfaces without forming a complex network. Solid samples of successive higher pressures were grown from superfluid under a mass flow field. We confirm the presence of mass flow through solid helium and find that the mass flow decreases with increasing temperature and decays exponentially with pressure. In contrast to the results from the University of Mass., we found mass flow continues up to 1 K and pressure above 30 bar. [Preview Abstract] |
Tuesday, March 14, 2017 9:24AM - 9:36AM |
E20.00008: Mass Flux Measurements in Solid 4He Valentyn Rubanskyi, R.B. Hallock There has been considerable attention given to solid helium over the past decade. Our approach to study the solid has been to sandwich solid helium between two reservoirs of superfluid helium. With this approach, we previously found and explored the characteristics of mass flux that takes place from one reservoir to the other through the solid-filled experimental cell off the melting curve (1). We observed flow that has characteristics that appear to match expectations for one-dimensional conductivity (2) and we have documented the effects that various concentrations of 3He impurity have on the temperature dependence of the flow (3). These experiments continue and we expect to report on new results that may be available that are aimed at placing constraints on what carries the observed mass flux. (1) M.W. Ray and R.B. Hallock, Phys. Rev. Letters 100, 235301 (2008); 105, 145301 (2010); Phys. Rev. B 79, 224302 (2009). (2) Ye. Vekhov and R.B. Hallock, Phys. Rev. Letters 109, 045303 (2012); Phys. Rev. B 90, 134511 (2014). (3) Ye. Vekhov, W.J. Mullin and Hallock, Phys. Rev. Letters 113, 035302 (2014); Ye. Vekhov and R.B Hallock, Phys. Rev. B 92, 104509 (2015). [Preview Abstract] |
Tuesday, March 14, 2017 9:36AM - 9:48AM |
E20.00009: Effect of Rotation on Elastic Moduli of Solid Helium Keiya Shirahama, Tomoya Tsuiki, Daisuke Takahashi, Satoshi Murakawa, Yuichi Okuda, Kimitoshi Kono The response of torsional oscillator (TO) containing solid helium to the rotation was strong evidence for a possible supersolid phase. However, many experiments without rotation show that TO response comes from the change in the elasticity of solid, not from supersolidty. This situation calls for experiment for studying the elasticity of solid helium under rotation. If the elasticity of solid helium is affected by rotation, TO response under rotation may be also explained by the elasticity of solid helium.We performed direct measurements of elasticity of solid helium under rotation. We used quarter-circle shape PZT transducers and measured the shear and Young’s moduli of annular solid samples. When we applied sufficiently low strain, the shear modulus was independent of rotation velocity. On the other hand, when we applied high strain, we observed a decrement of shear modulus at most 16 $\%$ at rotation of 4 rad/s of the total change without rotation. But it seems difficult to explain TO result by our result due to the different scale of strain applying to solid in each measurement.We will discuss the result in terms of a dislocation model which is often referred to describe the elastic property of solid helium. [Preview Abstract] |
Tuesday, March 14, 2017 9:48AM - 10:00AM |
E20.00010: Development of a Planar Josephson Junction for Helium-4 Jeffrey Botimer, Eunjong Kim, Benjamin King, Keith Schwab We are investigating the transport of superfluid helium-4 through a two dimensional, nano-porous polymer material in the temperature interval 300mK to {\$}T\textunderscore $\backslash $lambda{\$}. The crystalline material is covalently bonded, a single molecule thick, and supported on a 50nm silicon nitride frame, covering a two-micron aperture. We expect this junction structure to realize a weak-link for temperatures far below the superfluid transition temperature, leading to much larger critical current densities than previously demonstrated junctions which operate very close to {\$}T\textunderscore $\backslash $lambda{\$} where the superfluid density and resulting mass current is greatly reduced. We expect this junction to lead to ultra-sensitive superfluid interferometers with the sensitivity beyond that of atomic matter wave interferometers and the sensitivity to resolve the fluctuations in the Earth rotation in a hand-sized device. [Preview Abstract] |
Tuesday, March 14, 2017 10:00AM - 10:12AM |
E20.00011: Puzzling KT onset slope from third sound measurements with layered helium films on carbon nanotubes Gary Williams, Emin Menachekanian, Vito Iaia, Mingyu Fan, Chaowei Hu, Fufang Wen Third sound measurements of thin ^$^4$He films adsorbed on multiwall carbon nanotubes 10 nm in diameter show layer-completion effects at 3, 4, and 5 atomic layers. Temperature sweeps at fixed film thickness show Kosteritz-Thouless onset behavior (a sudden rise in dissipation), but a puzzle is that the slope of the onset temperature with film thickness is only about 1/2 of the KT universal vaue. Speculation about the role of carbon-atom induced modulation of the film thickness will be discussed [Preview Abstract] |
Tuesday, March 14, 2017 10:12AM - 10:24AM |
E20.00012: Torsional Oscillator Study of Gap-Induced Elasticity of $^4$He Films on Disordered Substrate Takahiko Makiuchi, Michihiro Tagai, Yusuke Nago, Keiya Shirahama We report torsional oscillator (TO) studies of the superfluid-insulator transition in $^4$He films absorbed on disordered substrate. $^4$He films are superfluid above a critical coverage $n_{\rm c}$. Below $n_{\rm c}$, an energy gap opens between two distinct states of adatoms; the localized (insulating) state, in which the adatoms are bound to the substrate, and the extended state, in which they can move freely. Previous TO measurements in which a porous Gelsil glass was located in the torsion bob showed an anomalous response at lower temperature in the insulating phase. This was interpreted as a stiffening of $^4$He film. To measure directly the elasticity, we have begun a new TO study. The TO has a Gelsil glass torsion rod and a dummy bob. We have clearly observed a change in the resonant frequency and an energy dissipation peak, which are originated from a change in shear modulus of adsorbed He film. The temperature dependence of the resonant frequency and the dissipation agrees well with those in the previous TOs at the same coverage. Results definitely conclude a crossover between ``stiff" and ``soft" states of $^4$He films governed by a coverage dependent energy gap in the insulating phase. [Preview Abstract] |
Tuesday, March 14, 2017 10:24AM - 10:36AM |
E20.00013: Measurements on Decay of Grid Turbulence in Superfluid $^4$He in a Large Square Channel Jihee Yang, Gary G. Ihas Grid turbulence in superfluid $^4$He is investigated over a temperature range from 1.5 to 2.1 K with different grid velocities. The attenuation of second sound is observed across a large channel (4.6 cm x 4.6 cm square) and analyzed to obtain vortex line density ($L$) over time. A novel phase and amplitude locked tracking system is used to minimize frequency shift effects on resonant peaks in the cavity caused by temperature fluctuations. A grid turbulence theory predicts that vortex line density decay as $L\sim$t$^{-11/10}$ or t$^{-17/14}$ in early times when the energy containing eddies increase from the length scale of the grid mesh. At later time, when the energy containing eddy size become comparable to the channel size, the vortex line density is expected to decay as $L\sim$t$^{-3/2}$ consistent with classical result\footnote{S. R. Stalp, L. Skrbek, and R. J. Donnelly, Phys. Rev. Lett. 82, 4831 (1999)}. We present results in decay of vortex line density from the large channel: evidence for t$^{-11/10}$ is observed partially for early time and t$^{-2}$ instead of t$^{-3/2}$ is observed for later time. A consistent bump/plateau feature is observed in between the two decay regions that is not explained from the theory. [Preview Abstract] |
Tuesday, March 14, 2017 10:36AM - 10:48AM |
E20.00014: Entanglement area law in superfluid $^4$He C. M. Herdman, P.-N. Roy, Roger Melko, Adrian Del Maestro Area laws were first discovered by Bekenstein and Hawking, who found that the entropy of a black hole grows proportional to its surface area, and not its volume. Entropy area laws have since become a fundamental part of modern physics, from the holographic principle in quantum gravity to ground state wavefunctions of quantum matter, where entanglement entropy is generically found to obey area law scaling. As no experiments are currently capable of directly probing the entanglement area law in naturally occurring many-body systems, evidence of its existence is based on studies of simplified theories. Using new exact microscopic numerical simulations of superfluid $^4$He, we demonstrate for the first time an area law scaling of entanglement entropy in a real quantum liquid in three dimensions. We validate the fundamental principles underlying its physical origin, and present an ``entanglement equation of state" showing how it depends on the density of the superfluid. [Preview Abstract] |
Tuesday, March 14, 2017 10:48AM - 11:00AM |
E20.00015: Effective Hubbard model for Helium atoms adsorbed on a graphite Yuichi Motoyama, Akiko Masaki-Kato, Naoki Kawashima Helium atoms adsorbed on a graphite is a two-dimensional strongly correlated quantum system and it has been an attractive subject of research for a long time. A helium atom feels Lennard-Jones like potential (Aziz potential [1]) from another one and corrugated potential from the graphite [2]. Therefore, this system may be described by a hardcore Bose Hubbard model with the nearest neighbor repulsion on the triangular lattice, which is the dual lattice of the honeycomb lattice formed by carbons. A Hubbard model is easier to simulate than the original problem in continuous space, but we need to know the model parameters of the effective model, hopping constant t and interaction V. In this presentation, we will present an estimation of the model parameters from ab initio quantum Monte Carlo calculation in continuous space in addition to results of quantum Monte Carlo simulation for an obtained discrete model. [1] R. A. Aziz, V. P. S. Nain, J. S. Carley, W. L. Taylor and G. T. McConville, J. Chem. Phys. 70, 4330 (1979). [2] W. E. Carlos and M. W. Cole, Surf. Sci. 91, 339 (1980). [Preview Abstract] |
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