J. B. Kycia

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.

Low field DC SQUID nuclear magnetic resonance on single crystal UPt3

Abstract A SQUID spectrometer is being used to study high-quality single crystals of UPt 3 in low magnetic fields by performing pulsed NMR on 195 Pt. The system uses a multiloop DC SQUID with additional positive feedback and operates in flux-locked loop mode from DC to 3 MHz. It has an overall coupled energy sensitivity of 800 h and a dead time of ∼5 μs. NMR signals from UPt 3 have been observed in both the superconducting mixed state and in the normal state. A bulk platinum marker is used to determine the magnetic field. Measurements of 195 Pt Knight shifts in UPt 3 are reported.

Low-frequency broadband NMR on UPt3 using DC SQUIDs

Abstract An NMR spectrometer has been constructed based on a DC SQUID with additional positive feedback, operating in flux locked loop mode. The system has an overall bandwidth of 3MHz and a coupled energy sensitivity of 800 h . The spectrometer is being used to study high-quality single-crystal samples of UPt 3 , in order to investigate the superconducting order parameter. NMR signals have been observed in the superconducting mixed state at significantly lower frequencies than hitherto, down to 100 kHz.

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.

The growth and characterization of high quality UPt3 crystals

Single crystals of UPt3 have been prepared. The crystals are shown to have a superconducting transition temperature of 526±2 mK with a transition width of 12.6 ± 0.1 mK. The measured x-ray rocking curve FWHM of the (002) peak is 180 ± 5 arcseconds, compared to a theoretical minimum linewidth as predicted for a perfect UPt3 single crystal of 90 arcseconds. The x-ray characterization, susceptibility, residual resistivity ratio (RRR) and impurity concentration results are presented.

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 study of the UPt3 superconducting phases

Abstract In order to distinguish the UPt3 superconducting (s.c.) phases we have studied their magnetic properties at low fields in a SQUID magnetometer and up to fields >Hc2(0) with a capacitive torque-meter. With the SQUID we measure the magnetic penetration depth and find the second s.c. transition at Tc− when the field is applied along the c-axis, but not with H ⊥ c . This result, combined with power-law behavior at low temperature T, is most consistent with the two-dimensional E2u s.c. order parameter. Below 20 mK we find an additional diamagnetic signal that we ascribe to the normal state magnetism. In high fields our torque measurements show a kink of the perpendicular magnetization component at the B–C phase line, pointing to an enhanced Ginzburg–Landau parameter in the C phase.