H. H. Hensley

Measurement of the magnetic susceptibility of normal fluid3He at very low temperatures

We present pulsed NMR measurements of the low temperature (≈0.003 K) magnetic susceptibility of normal liquid3He as a function of pressure. Our results agree well with the extrapolation from 0.035 K of the data of Ramm et al. We calculate new values for the Fermi liquid parameter F0a using the heat capacity data of Greywall.

High-resolution acoustic measurements in fluids and gases by a path length modulation technique

An acoustic technique has been developed that permits high-resolution velocity measurements to be performed in liquids and gases under circumstances where the acoustic attenuation may become very large. This cavity resonance method has been demonstrated in cavities with lengths as small as 150 µm at acoustic frequencies up to 151 MHz. The acoustic path length is continuously adjusted by a piezoelectric bimorph controlled by feedback from a sensitive acoustic impedance spectrometer. The measurement of velocity then simply reduces to measurement of position of the bimorph, and this can be performed with high accuracy using a capacitance bridge. Absolute measurements of the attenuation of sound can also be performed with this arrangement. It is suggested that this approach will be useful for the study of collective excitations in quantum fluids.

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.

Accurate determination of the Landau parameter F o a for3He

Results of measurements of the low temperature magnetic susceptibility of normal liquid3He have been performed as a function of pressure from which we have calculated the Fermi Liquid parameter Foa.

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.

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.

Abrupt dimensional crossover in the quasi-one dimensional conductor, H2(pc)I

Abstract H2(pc)I is known to have highly anisotropic electronic and structural properties. Electrical conductivity and magnetoresistance measurements have been performed on high purity H2(pc)I single crystals ranging from room temperature to 20 mK in magnetic fields up to 5.5 tesla. We have observed abrupt changes in both measurements around 2 K. Conductivity follows a simple quadratic temperature dependence below 2 K and remains metallic (≈10000 ω-1cm-1) down to very low temperatures, 20 mK. This phenomenon has not been reported previously in quasi-one dimensional conductors. We suggest that H2(pc)I experiences an abrupt dimensional crossover from a 1 dimensional regime to a 3 dimensional one below 2 K.

High-resolution acoustic measurements by path length modulation

Abstract An acoustic technique is described which permits precise measurement of phase velocity in liquids or gases with high attenuation ( α >10 cm −1 ) utilizing a thin, variable path length acoustic cavity formed by a quartz transducer and a piezoelectric bimorph. The path length can be changed manually or in feedback where the bimorph motion is driven by the output of a cw spectrometer. Measurement of phase velocity is then simply measurement of cavity size, which is done capacitively to high precision. The path length modulation method can allow absolute measurement of attenuation as well as resolution of ∼10 −5 in phase velocity with a path length as short as 50μ. It is anticipated that this approach can be used successfully to explore regimes of collective modes and pair breaking in superfluid 3He, as well as textural effects in restricted geometries.