Giant thermomechanical effect in normal liquid 3He

Abstract

Measurements are presented of the thermomechanical coefficient of normalliquid 3He confined in a porous plug preplated with four monolayersof 4He. These nonmagnetic monolayers displace the magnetic solid-like3He monolayers that are adjacent to the pore surfaces when the plugis filled with pure 3He. In the low-temperature limit (T <= 10mK) the coefficient can be described by Δ P/Δ T ~ s/6vwhere Δ P is the pressure difference across the plug generated bythe temperature difference Δ T, and s and v are the molarentropy and molar volume. This low-temperature limit corresponds to thecondition d <<lq where d is the pore diameter and lq isthe bulk liquid 3He quasiparticle mean free path; that is, thequasiparticles are predominantly boundary scattered in the pores. Themeasured coefficient is half that calculated by Edwards Culman and He. When compared with this new experimental result for the 4He-platedporous plug, the earlier result for pure liquid 3He is strikinglylarger (by up to 30x at 2~mK). This enhancement is reminiscent ofthe giant thermopowers measured in Kondo and other dilute magneticalloys. It is speculated that the enhanced thermomechanical coefficientfor pure liquid 3He is due to magnetic scattering of the 3Hequasiparticles by the two magnetic solid-like 3He monolayers adjacentto the pore surfaces. PACS Nos.: 67.55.-s and 67.55.Hc