Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Y23: Quantum Fluids and Solids |
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Sponsoring Units: DCMP Chair: Robert Hallock, University of Massachusetts Amherst Room: C125-C126 |
Friday, March 19, 2010 8:00AM - 8:12AM |
Y23.00001: Dynamics of a quantum vortex Lara Thompson, Philip Stamp Quantum vortex dynamics remain poorly understood despite decades of theoretical investigation. The vortex is a topological soliton, arising from the same medium as the environmental modes with which it interacts. We find non-trivial orthogonality relations between these environmental modes and the vortex zero mode. Depending on whether they are satisfied or not, we predict vastly different low temperature vortex dynamics. We present a model system where orthogonality is upheld. The environment is integrated out, including interference effects from opposite chirality environmental modes, yielding the low temperature vortex dynamics. These turn out to be highly non-local at low T. [Preview Abstract] |
Friday, March 19, 2010 8:12AM - 8:24AM |
Y23.00002: Frequency Dependence of Ultrasound Attenuation in Superfluid $^{3}$He in Aerogel Byoung Hee Moon, Naoto Masuhara, Pradeep Bhupathi, Miguel Gonzalez, Mark Meisel, Yoonseok Lee, Nobert Mulders Longitudinal ultrasound measurements have been performed in superfluid $^{3}$He impregnated in 98{\%} aerogel. The attenuation measured at four frequencies between 3.69 and 11.3 MHz shows an interesting feature in the zero temperature limit. Due to the limitation of the mean free path by the aerogel, the first sound regime persists to zero temperature, following the natural expectation of $\omega ^{2}$-dependence of the attenuation for the entire temperature range. However, deviations from the $\omega ^{2}$-dependence were observed, exhibiting progressive development towards higher pressure and lower temperature. We argue that this feature is directly related to the impurity states in the gap of the superfluid $^{3}$He in aerogel and expect that the measurements in a finer and wider frequency range could reveal the details of the gap structure in this system. [Preview Abstract] |
Friday, March 19, 2010 8:24AM - 8:36AM |
Y23.00003: The Suppression of the B-like Phase of Superfluid $^{3}$He in Aerogel by Magnetic Fields Yoonseok Lee, Byoung Hee Moon, Naoto Masuhara, Pradeep Bhupathi, Miguel Gonzalez, Mark Meisel, Nobert Mulders The phase diagram of superfluid $^{3}$He in 98 {\%} aerogel has been determined as a function of the pressure (P), temperature (T), and magnetic field (H). The transition features were identified in longitudinal ultrasound attenuation. The sound attenuation was measured at five pressures (14 $\sim $ 33 bar) and four frequencies between 3.6 and 11.3 MHz in the presence of magnetic fields up to 4.5 kG. The superfluid transition is marked by a rather rapid change in attenuation at the normal liquid to superfluid phase transition. The A-B like phase transition appears as a smooth jump in attenuation. We found that the B-like phase in aerogel is suppressed in a completely different manner than in bulk, indicating that the poly-critical point is indeed pushed up in pressure and the anisotropic scattering plays an important role in this system. [Preview Abstract] |
Friday, March 19, 2010 8:36AM - 8:48AM |
Y23.00004: Superfluid transition in granular 4He: Coupling and proximity effects Justin Perron, Mark Kimball, Kevin Mooney, Francis Gasparini We report measurements of the specific heat and superfluid density of helium confined in an array of (2 $\mu$m)$^3$ boxes in equilibrium with a 31.7~nm film. We identify for the first time with these data proximity effects on the specific heat and superfluid density of the film. Comparison with other data allows us to deduce the excess specific heat associated with a collective behavior near the superfluid transition in an array of (1 $\mu$m)$^3$ boxes of helium connected through channels. Some of these effects are analogous to the behaviour of superconductors but have not been identified previously in the case of $^4$He. [Preview Abstract] |
Friday, March 19, 2010 8:48AM - 9:00AM |
Y23.00005: Quantum Monte Carlo Studies of Luttinger Liquids Adrian Del Maestro An experimental realization of a bosonic Luttinger liquid may possibly be found in systems where helium-4 has been confined to narrow nanopores with large aspect ratios. We have employed worm algorithm path integral quantum Monte Carlo methods to study low dimensional strongly interacting bosonic systems at finite temperature in the grand canonical ensemble. The resulting numerical data can be used in conjunction with scaling predictions from Luttinger liquid theory to aid in the experimental search. [Preview Abstract] |
Friday, March 19, 2010 9:00AM - 9:12AM |
Y23.00006: Photoionization dynamics of pure helium droplets: exciton formation vs autoionization Oleg Kornilov, Oliver Gessner, Oliver Buennermann, Chia Wang, Steve Leone, Daniel Neumark $^4He$ droplets possess unique properties. In addition to fundamental quantum effects of superfluidity the droplets show ability to efficiently pick-up foreign atoms, molecules and complexes, which is used in a number of matrix isolation spectroscopies in energy domain. Complementary to these studies, novel time-domain experiments will be presented emphasizing dynamics of photoionization of pure helium droplets. The experiments follow up on a recent observation of ultraslow (E$<1$ meV) photoelectrons emitted from droplets upon ionization by synchrotron radiation. The dynamics of photoionization is studied by exciting droplets with a pulsed VUV radiation generated using the high-order harmonic generation technique. The droplets subsequently interact with an IR pulse, which probes transient electronic states before droplet autoionization. Femtosecond and picosecond relaxation dynamics and competition between droplet ionization and formation of a long-lived excited state are observed. Probe pulse leads to droplet ``re-excitation'' and production of even more ultraslow electrons. The results will be extended to doped droplets anticipating indirect dopant ionization dynamics. [Preview Abstract] |
Friday, March 19, 2010 9:12AM - 9:24AM |
Y23.00007: Thermal and quantum crystallizations of $^4$He in aerogel Ryuji Nomura, Ken-ichi Ueno, Ryota Masumoto, Yuichi Okuda The way of the crystallization of $^4$He in aerogel was known to show a dynamical phase transition due to the competition between thermal fluctuation and disorder: crystals grow via creep at high temperatures and via avalanche at low temperatures (Phys. Rev. Lett. 101, 175703 (2008)). Here we report the growth velocity and the crystallization pressure of $^4$He in both regions. In the creep region, crystal growth is faster at higher temperature and becomes slower with cooling. This is consistent with the expectation that crystal growth is via a thermally activated interface motion in the disordered media in the creep region. This temperature dependence is opposite to the bulk crystal growth. Growth velocity is the lowest at the transition temperature. In the avalanche region, it slightly increases with cooling and saturates at lower temperature. This temperature independent growth is presumably the result of the macroscopic quantum tunneling through the disorder. The crystallization pressure in aerogel is not just like a shift of the bulk crystallization pressure but has a maximum at the transition temperature. [Preview Abstract] |
Friday, March 19, 2010 9:24AM - 9:36AM |
Y23.00008: Growth of Solid $^4$He from the Superfluid Robert Hallock, Michael Ray We have previously reported on the observation of random, transient events during the growth of solid $^4$He crystals from the superfluid at constant temperature [1,2]. The solid is grown by injecting mass into an experimental cell [2] through two Vycor rods, which allows us to continue to add mass to the solid at pressures greater than the bulk melting pressure. The observed events occur at pressures greater than the melting pressure, but less than $\sim 26$ bar, and are seen as drops in pressure (measured at the ends of the solid), $\Delta P \leq$ 150 mbar, accompanied by temperature transients, $\Delta T \leq$ 9 mK. These events may be the solidification of meta-stable liquid regions embedded in the solid that were at the same pressure as the solid. Additional analysis now includes the possibility that the liquid regions are instead at the melting pressure, and that there exists a strain field in the solid which disappears when the liquid solidifies. We will show examples of these events, and report on this new analysis. Our experiments are supported by the NSF via DMR 08-55954. \\ \\ $[1]$ M.W. Ray and R.B. Hallock, J. Phys.: Conf. Ser. \textbf{150}, 032088 (2009).\\ $[2]$ M.W. Ray and R.B. Hallock, Phys. Rev. B \textbf{79}, 224302 (2009). [Preview Abstract] |
Friday, March 19, 2010 9:36AM - 9:48AM |
Y23.00009: Thermal Quenching and Pressure Gradients in Solid Helium Abdul Suhel, John Beamish Torsional oscillator measurements on solid $^{4}$He show a frequency increase at low temperatures that suggests mass decoupling or ``non-classical rotational inertia'' (NCRI). The magnitude of the NCRI varies from about 0.02{\%} to 20{\%} in different oscillators, although the temperature dependence is essentially the same. The amount of mass which decouples appears to be larger when the helium is frozen and cooled rapidly. Annealing at high temperatures usually reduces the NCRI, with an accompanying drop in pressure, suggesting that defects are involved. We have built a cell to measure the temperature dependence of the pressure and the magnitude of pressure gradients in solid helium. The helium can be melted in a few seconds using a heater embedded in the crystal and can be refrozen and quenched to low temperature in about 10 seconds. From the maximum pressure differences in the cell, we infer a yield stress of order 0.1 bar for solid $^{4}$He. The pressure gradients relax when the temperature is raised above about 0.5 K. We describe the temperature dependence of this annealing process. [Preview Abstract] |
Friday, March 19, 2010 9:48AM - 10:00AM |
Y23.00010: Low Temperature Pressure Gauge Based on a Quartz Tuning Fork F. M. Huisman, E. Van Cleve, D. Miller, P. Taborek Experiments in our lab on the phases of helium films on alkali metal substrates require a low temperature in situ pressure gauge. The damping of a high quality factor (Q) mechanical oscillator is strongly affected by the background gas pressure, which can be utilized to make a pressure transducer. We have investigated this effect using quartz tuning forks with a resonant frequency of 32 kHz. The variation of the Q was measured as a function of temperature from 300 to 1K and pressure from 0 to 10 torr. A clear transition between ballistic and viscous dissipation was observed. We will discuss the linearity of the oscillators as a function of drive amplitude, the resolution of the pressure gauge and various electronic and data processing strategies for dealing with relatively low frequency oscillators with Q $>$ 1 million. [Preview Abstract] |
Friday, March 19, 2010 10:00AM - 10:12AM |
Y23.00011: Turbulant heating in superfluid He$^4$ K.J. Thompson, S.C. Liu, G. Labbe, G.G. Ihas Turbulence leads to heating in classical fluids, via viscus damping. Current theories predict the time-dependent evolution of heat due to decaying turbulence in a pure (inviscid) superfluid ($^4$He near absolute zero). Measurement of such a rise in temperature as a function of time will provide insight into the energy dissipated by the fluid and the time scales involved in the decay process. We have detected a rise in helium temperature as a resulting from a sudden motion of a stainless steel grid out of a column of superfluid He$^4$. The temperature rise was measured by a 300 $\mu$m Ge thermometer submersed in the fluid. We have compared our measurements to an identical system without the stainless steel grid. The heating patterns due to the grid motion is measured, examined and discussed, with data presented for the total energy dissipated in the fluid as well as the energy rise in the fluid as a function of time. The heat from turbulent decay is evident. This work was supported by the Research Corporation and the US National Science Foundation grant \# DMR-0602778. [Preview Abstract] |
Friday, March 19, 2010 10:12AM - 10:24AM |
Y23.00012: The effects of screening parameter on Edgemagnetoplasmons Mehmet Goksu We report a study of dependence of Edgemagnetoplasmons on screening parameter on a helium surface. A finite field is used since it is difficult to extract the signal from crossing of many right and left handed edge modes near zero magnetic field. We find that the change in frequency is in agreement with a change in electron pool radius. A qualitative comparison between our experimental results and theory is given. [Preview Abstract] |
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