NMR measurements on dilute solutions of3He in solid4He

Abstract

Measurements of the spin diffusion coefficientD and relaxation timesT1 andT2 are reported for3He impurity in solid4He of fractional concentrationx3 down to 10−4. Forx3≤10−3,T∼0.5 K, and molar volume 21.0 cm3,Dx3=1.2±0.4×10−11 cm2 sec−2,T2x3=1.7×10−4 sec, andT1x3=6.6×10−2 sec at 2 MHz. The spectral densityJ(ω) for dipole field fluctuations has been studied as a function of frequency from 104 to about 107 Hz. Two branches of approximately equal area have been found with scaling frequencies of about 104 and 106 Hz. It is argued that the high-frequency branch, which has some unusual structure, relates to3He-4He tunnelling, uninhibited by other3He impurities, and occurs at a rate of about 0.6 MHz for molar volume 21 cm3. The molar volume dependence of this tunneling appears to be similar to that found in pure, solid3He.