Low field study of A-like phase for superfluid 3He in aerogel

UnrestrictedLongitudinal and transverse DC-SQUID NMR experiments have been carried out to study the A-like phase of the superfluid 3He in the presence of aerogel scattering. Because the wide spectral line width of the scattered 3He A-like signals, the longitudinal response can not be identified from the background noise in the current experimental setup. The Fermi liquid to 3He A-like phase transition temperature Tc,aero have been inferred from the transverse NMR data only. Different from the previous 3He in aerogel experiments, which have mainly focused on the high field transverse NMR studies of the order parameter, the current low field NMR study gives a better physical picture of the impurity scattering effect on the superfluid order parameter. The field scaling measurement of the A-like phase frequency shift is carried out for the static H0 field at 10.31, 20.44 and 40.12 Gauss with the superfluid pressurized at 27.58 bar. For magnetic fields at 20.44 and 40.12 Gauss, the aerogel signal shifting away from the Larmor frequency is easily identified from the data analysis. But for magnetic field at 10.31 Gauss, the signal is much less visible in the FFT spectrum. Several DSP algorithms, including Morlet wavelet, Welch periodogram and Wiener analysis, have been carried out to further investigate the time-frequency response of the signal.; The 3He superfluid magnetic response is taken with 3 monolayers of 4He coated on the nominal 99.7% porosity aerogel strands. The purpose of the 4He preplating is to eliminate the fast exchange interactions between the superfluid and localized magnetic moments due to the 3He atoms deposited on the surface. The results from the bulk A phase transition are used to determine the absolute temperature scales for the experiment. A least square fit to the real time data is used to extract the normal fluid magnetic responses. Afterwards, the 3He superfluid A-like signal due to the presence of aerogel impurities is analyzed to determine the Tc,aero at 27.58 bar. The suppression of the superfluid order parameter is compared to the experimental results at high fields from other groups