Naoto Masuhara

Scattering of /sup 4/He atoms grazing the liquid-/sup 4/He surface

Measurements of the scattering of /sup 4/He atoms grazing the surface of liquid /sup 4/He show that the reflectivity approaches unity as the perpendicular wave vector tends to zero, in agreement with theoretical predictions.

Energy distributions of trapped atomic hydrogen

Progress on magnetic confinement and evaporative cooling of spin-polarized atomic hydrogen is described, and the first results are presented for the energy distribution of the trapped gas. Data are displayed for energy distributions during various stages of cooling. For the lowest temperature studied the results are in good agreement with the calculated distribution for a temperature of 800 μK.

Spin diffusion of a two-dimensional electron gas in the random phase approximation

Abstract Spin transport properties of spin-polarized two-dimensional electron gas are studied in the presence of electron–electron interactions. Longitudinal and transverse spin diffusion coefficients are calculated with the quantum transport equation. New results are obtained by evaluating both the drift and the collision terms using the random phase approximation, while the drift term was calculated by Hartree–Fock approximation in our earlier work. The qualitative features remain same, but the present work is valid for larger polarizations. We find that the e–e scattering, which does not contribute to the charge drift mobility, has a significant contribution to the spin diffusion.

Spin transport properties in two-dimensional electron gas

Abstract Spin transport properties of spin-polarized two-dimensional electrons are studied, with application to heterostructures of III–V semiconductors. Spin diffusion coefficients are obtained by numerically solving a quantum transport equation. It is shown that the ‘spin-rotation term’, which leads to anomalous spin diffusion and spin waves in three-dimensional spin polarized 3 He and hydrogen, is also present in two-dimensional degenerate electron systems at low temperatures. Longitudinal and transverse spin diffusion coefficients show different temperature dependence due to the fact that the phase space available in electron–electron scatterings associated with each diffusion process is different.

Pulsed Fourier-Transform Ultrasonic Spectroscopy for Ultralow Temperature Applications

Pulsed Fourier-Transform (FT) ultrasonic spectroscopy has been developed for the purpose of studying 3He at ultralow temperatures. Our method is analogous to pulsed FT NMR and possesses several advantages over conventional time-of-flight acoustic techniques. For use at low temperatures, the most significant advantage is the ability to observe the frequency spectrum while the temperature, pressure, and magnetic field may be independently tuned. More specifically, using longitudinal LiNbO3 transducers operating both on- and off-resonance, we are able to study several broadband windows of frequency, namely 16–25 MHz, 60–70 MHz, and 105–111 MHz. The determination of the energy gap of 3He-B is presented as an effective application, and other novel uses are discussed.

Ultrasound attenuation of superfluid 3He in aerogel.

We have performed longitudinal ultrasound (9.5 MHz) attenuation measurements in the B phase of superfluid 3He in 98% porosity aerogel down to the zero temperature limit for a wide range of pressures at zero magnetic field. The absolute attenuation was determined by direct transmission of sound pulses. Compared to the bulk fluid, our results revealed a drastically different behavior in attenuation, which is consistent with theoretical accounts with gapless excitations and a collision drag effect.

Zero Sound Attenuation Near the Quantum Limit in Normal Liquid 3He Close to the Superfluid Transition

The zero sound attenuation of normal liquid 3He has been studied over a range of temperatures from slightly above the superfluid transition temperature, Tc, to approximately 10 mK at the constant pressures of 1 and 5 bar. Using longitudinal LiNbO3 transducers, operating both on and off resonance, the experiment was performed at 15 discrete frequencies located in several broadband frequency windows, including 16–25, 60–70, and 105–111 MHz. The results are compared to Landaus prediction for the attenuation of zero sound in the quantum limit, (kBT≪ħω≪kBTF), where α0(P,T, ω)= α′(P) T2{1+(ħω/2πkBT)2}. Calibration of the received zero sound signals was performed by measuring the temperature dependence of the first sound attenuation from 30 to 800 mK at those same frequencies and pressures. The data are compared to previous results.

Ultrasound attenuation and aP−B−Tphase diagram of superfluidH3ein 98% aerogel

Longitudinal sound attenuation measurements in superfluid 3He in 98% aerogel were conducted at pressures between 14 and 33 bar and in magnetic fields up to 4.44 kG. The temperature dependence of the ultrasound attenuation in the A-like phase was determined for the entire superfluid region exploiting the field induced meta-stable A-like phase at the highest field. In the lower field, the A-B transition in aerogel was identified by a smooth jump in attenuation on both cooling and warming. Based on the transitions observed on warming, a phase diagram as a function of pressure (P), temperature (T) and magnetic field (B) is constructed. We find that the A-B phase boundary in aerogel recedes in a drastically different manner than in bulk in response to an increasing magnetic field. The implications of the observed phase diagram are discussed.

NMR Characterization of 3He Nanoclusters Embedded in hcp 4He

The properties of 3He nanoclusters in phase-separated solid 3He-4He mixture were investigated using pulse NMR. Samples of pressure between 2.64 and 3.71 MPa and NMR frequencies, 62.5, 125, and 250 kHz were used. Magnetization was measured in the temperature range between 0.6 to 10 mK. The solid-like fraction was obtained from the relative magnitudes of magnetization and it showed a sharp increase with pressure around 2.94 MPa accompanying an abrupt change in Weiss temperature. For samples of pressure between 2.94 and 3.15 MPa, the magnetization could be separated into two components with different spin-spin relaxation time T*2s. The short and long T*2 components showed ferromagnetic and antiferromagnetic tendencies, respectively. The long component showed an anomalous decrease of magnetization below 1.05 mK.

Stability of electrical self-oscillation in PANi-CSA/PMMA composites

Abstract Self-electrical oscillations in composites of 8% PANi-CSA in PMMA reported earlier have been seen in different samples. While the earlier samples showed a transition from very regular to chaotic behavior depending upon bias current, the new samples exhibit time evolution with an initial amplitude growth of the oscillations followed by steady smaller amplitude oscillations, gradually diminishing for most conditions. Very different detailed behavior in similarly prepared samples has been observed and are compared.