Interaction-Assisted Reversal of Thermopower with Ultracold Atoms

Abstract

We study thermoelectric currents of neutral, fermionic atoms flowing through a mesoscopic channel connecting a hot and a cold reservoir across the superfluid transition. The thermoelectric response results from a competition between density-driven diffusion from the cold to the hot reservoir and the channel favoring transport of energetic particles from hot to cold. We control the relative strength of both contributions to the thermoelectric response using an external optical potential in both non-interacting and strongly-interacting systems. Without interactions, the magnitude of the particle current can be tuned over a broad range but is restricted to flow from hot to cold in our parameter regime. Strikingly, strong interparticle interactions additionally reverse the direction of the current. We quantitatively model ab initio the non-interacting observations and qualitatively explain the interaction-assisted reversal by the reduction of entropy transport due to pairing correlations. Our work paves the way to studying the coupling of spin and heat in strongly correlated matter using spin-dependent optical techniques with cold atoms.

Generation of spin currents by a temperature gradient in a two-terminal device

“…Later, the particle current might be reversed due to the difference in the particle number between two reservoirs, and, eventually, the system will come to a thermal equilibrium. We note that the timescale of particle transfer can be tuned in these experiments [14,39]. In particular, this timescale can be made comparable or smaller than the timescale associated with spin transfer in small strongly interacting one-dimensional systems, which is typically FIG.…”