Giant Thermomechanical Effect in Normal Liquid He-3

TL;DR

This study measures the thermomechanical coefficient of normal liquid He-3 in porous media, revealing a giant enhancement at low temperatures likely due to magnetic scattering effects, with implications for understanding quantum fluids.

Contribution

The paper provides the first detailed measurement of the thermomechanical coefficient in He-3 confined in porous media, showing a significant enhancement compared to previous results and proposing magnetic scattering as a key mechanism.

Findings

The thermomechanical coefficient is significantly larger in pure He-3 than in He-4 plated samples.

At temperatures below 10 mK, the coefficient follows a specific relation involving entropy and volume.

The observed enhancement is similar to giant thermopowers in magnetic alloys.

Abstract

Measurements are presented of the thermomechanical coefficient of normal liquid He-3 confined in a porous plug pre-plated with four monoloyers of He-4. These non-magnetic monolayers displace the magnetic solid-like He-3 monolayers that are adjacent to the pore surfaces when the plug is filled with pure He-3. In the low temperature limit (T < 10 mK) the coefficient can be described by dP/dT ~ s/6v, where dP is the pressure difference across the plug generated by the temperature difference dT and s and v are the molar entropy and volume. This low temperature limit corresponds to the condition d << l_q, where d is the pore diameter and l_q is the bulk liquid He-3 quasiparticle mean free path; that is, the quasiparticles are predominantly boundary scattered in the pores. The measured coefficient is half that calculated by Edwards, Culman and He. When compared with this new experimental result for the He-4 plated porous plug, the earlier result for pure liquid He-3 is strikingly larger (by up to 30x at 2 mK). This enhancement is reminiscent of the giant thermopowers measured in Kondo and other dilute magnetic alloys. It is speculated that the enhanced thermomechanical coefficient for pure liquid He-3 is due to magnetic scattering of the He-3 quasiparticles by the two magnetic solid-like He-3 monolayers adjacent to the pore surfaces.