H3eSpin Diffusion Measurements inH

Abstract

3He spin diffusion measurements for 3He-4He mixture films on Nuclepore are reported as a function of 3He coverage for 0. 030</=T</=0.070 K. We report measurements for a constant 4He coverage of 5.0 bulk density atomic layers, with 3He coverages between 0.10 and 0.98 layers. We find that the 3He spin diffusion coefficient, as measured by Hahn spin echoes, has an unexplained maximum as a function of 3He coverage and that the temperature dependence is somewhat weaker than predicted. Comparison measurements are presented for the NMR relaxation times T1 and T2 and the magnetization over the same 3He coverage range.

Anomalous spin diffusion in3He films: Expected behaviour in two-dimensional Fermi liquids

“…These features could not be reproduced by standard theoretical predictions (Miyake andMullin 1983, 1984). In the work reported by Sheldon and Hallock (2000), care has been taken to guarantee that the 3 He ®lm forms a two-dimensional (2D) system of interacting fermions, with little in¯uence from the 4 He super¯uid ®lm that is below. Hence one should be able to account for the observed features using theoretical results from a 2D Landau theory.…”

“…where m h is the 3 He hydrodynamic mass, a s is the hard-core potential radius and n is the density, which is linearly related to the layer coverage D 3 in the experiment carried out by Sheldon and Hallock (2000). The expansion paramenter of the theory is gˆ¡‰ln …2ºna 2 s †Š ¡1 and, for coverages ranging from 0 to 0.8, g falls within the interval from 0 to 0.58.…”

“…z The precise value for this constant is easy to calculate: C0… ¶ †ˆº 2 =12, which is not very different from 3/4. } The fact that only the angle º contributes to this behaviour relates to the relatively large phase space taken by head-on collisions (Farinas et al 1999, 2000).where m h is the 3 He hydrodynamic mass, a s is the hard-core potential radius and n is the density, which is linearly related to the layer coverage D 3 in the experiment carried out by Sheldon and Hallock (2000). The expansion paramenter of the theory is gˆ¡‰ln …2ºna 2 s †Š ¡1 and, for coverages ranging from 0 to 0.8, g falls within the interval from 0 to 0.58.…”

“…These latter provided grounds for the recent observation of unexpected behaviour, whose main cause will be argued in the following to be a consequence of the two-dimensionalit y of a general system of fermions. In a recent letter, Sheldon and Hallock (2000) presented experimental results for spin diOE usion in a thin ®lm of 3 He on top of a super¯uid 4 He ®lm. The result for the spin diOE usion coe cient D spin as a function of the 3 He coverage D 3 shows an upturn followed by a saturation and a downturn, as D 3 is increased.…”

“…The results are shown in ®gure 1 compared with the experimental ®ndings of Sheldon and 722 P. F. Farinas y These are the known singularities that, in the attractive channel, signal the breakdown of the Fermi liquid scenario towards a Bardeen±Cooper±Schrieffer state. Hallock (2000). To ®t the experimental data of Sheldon and Hallock at the given temperatures, a choice of a sˆ0: 75 Ā was made.…”