M. R. Rand

First- and zero-sound velocity and fermi liquid parameter F2s in liquid3He determined by a path length modulation technique

We have measured the velocity of first- and zero-sound in liquid3He at 12.6 MHz over the pressure range of 0.6 to 14.5 bar using a path length modulation technique that we have recently developed. From these measurements, the pressure dependent value of the Fermi liquid parameter F2s was calculated and found to be larger at low pressure than previously reported. These new values of F2s indicate that transverse zero-sound is a propagating mode at all pressures. The new values are important for the interpretation of the frequencies of order parameter collective modes in the superfluid phases. The new acoustic technique permits measurements in regimes of very high attenuation with a sensitivity in phase velocity of about 10 ppm achieved by a feedback arrangement. The sound velocity is thus measured continuously throughout the highly attenuating crossover (ωτ ≈ 1) regime, even at the lowest pressures.

New NMR evidence: Can an axi-planar superfluid3He-A order parameter be ruled out?

Abstract We have measured transverse NMR in3He superfluid through a pressure range of 1 to 13 bar. A comparison of A and B-phase data is made through the NMR relations of Leggett, which serve as an indicator of the order-parameter structure of the A-phase. Deviation from these relations may indicate a continuous distortion of the traditional Anderson-Brinkman-Morel model toward the planar state. Our results are consistent with identification of the A-phase as the axial state.

Nuclear magnetic resonance of {sup 3}He superfluid confined in high porosity aerogel

We report pulsed nuclear magnetic resonance (NMR) measurements of the transverse frequency and magnetization of3 He confined in aerogel with 98.2% open volume porosity. A homogeneous superfluid phase is observed at pressures, P > 12 bar, accompanied by a sharp onset of frequency shifts showing little or no textural broadening; a result quite unexpected for3He confined in random porous media. The transition temperatures and order parameter are both significantly suppressed from their bulk values and the magnetization data indicate this low temperature phase is an equal-spin pairing superfluid. For NMR tipping angles greater than 40 ° the resonance frequency drops abruptly to the normal state value. This tip angle dependence is not consistent with either the bulk3He-A or3He-B superfluid phases.

High frequency acoustic measurements in liquid3He near the transition temperature

We have made accurate measurements of the phase velocity in liquid3He at 0.6 bar near Tc using a path length modulation technique. The frequency used in this measurement (113 MHz) is much higher than any of the collective mode frequencies and well above the threshold for pair-breaking, ω≫Δ and ω > 2Δ0. We have observed a sharp but small linear increase in the phase velocity below Tc and a small decrease from the expected behavior in the normal fluid region very close to the transition temperature.

NMR on superfluid3He in aerogel

The transition to superfluidity of3He in high porosity (98.2%) acrogel has been observed by nuclear magnetic resonance techniques. The onset of the transition at all pressures above 13 bar is marked by a sharp increase in NMR frequency similar to that observed in bulk3He-A. This suggests that the aerogel/superfluid phase is highly homogeneous although both the transition temperature, Tc, and the amplitude of the order parameter are substantially suppressed. The acrogel strands are ≈ 50Å in diameter, much smaller than the superfluid coherence length. Consequently, we have attempted to interpret our observations as an impurity scattering problem. Based on our measurements of the magnetic field dependence of Tc it appears that both magnetic and potential scattering play important roles where the magnetic scattering can be associated with solid3He on the aerogel surface. This is determined by isotopic exchange with4He, a process which appears to stabilize a new superfluid state similar to the bulk B-phase.

Measurement of the g-shift in superfluid3he-B

We have measured the g-shift in superfluid3He-B as a function of temperature above 0.5 mK at a pressure of 1.03 bar, and a frequency of 3.87 MHz. We compare our results with predictions of the quasi-classical and Ginzburg-Landau theories, and present values of the Fermi-liquid parameter F2a and the β-parameter β345.

Magnetic field suppression of3He superfluidity in aerogel

We report nuclear magnetic resonance (NMR) measurements of superfluid3He confined in 98% porosity aerogel*.3He superfluidity in aerogel has been identified as an equal-spin pairing superfluid with a transition temperature,Tc, suppressed from that of the bulk. In magnetic fields, 0.38≤H≤2.2 kOe,Tc is further suppressed by 61 ±1μK/kOe2 at 18.7 bar. Such a quadratic magnetic field dependence of the superfluid transition is unexpected for an equal-spin pairing state. The effects of small additions of4He on the NMR frequency shifts and on the phase diagram are described.

High resolution sound velocity measurement in liquid3He using path length modulation technique

Employing path length modulation technique, we are able to make high resolution sound velocity measurements (≈ 10 ppm) with a relatively short path length. We present new values ofF23 calculated from zeroand first-sound velocity measurements at 12.6 MHz in liquid3He over the pressure range of 0.6 to 14 bar. We also report a newly observed behavior in high frequency zero-sound velocity at 113 MHz near the superfluid transition temperature at 0.6 bar.

Pulsed NMR in superfluid3He-B

Abstract We have performed pulsed NMR experiments in superfluid 3 He-B under conditions of high H 0 and H 1 homogeneity in order to study non-linear spin dynamics. We made extensive measurements near the “magic” tipping angle in order to measure its temperature dependence. We report the discovery of new effects, including a small negative frequency shift at tipping angles close to, but slightly less than the “magic” tipping angle. We also discuss the evolution of the precession frequency as the system relaxes after the RF pulse.

Experimental determination of the3He-B g-shift pressure dependence

Abstract The superfluid 3 He-B g -shift has been measured at temperatures above 0.5 mK and at pressures between 1 and 21 bar, at a Larmor frequency of 3.89 MHz. The g -shift is found to be a linear function of the magnetic susceptibility. The Ginzburg-Landau free energy expansion parameter β 345 , and the dipole energy coefficient a are obtained. Deviation from the weak coupling limit with increasing pressure is observed.