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 a nearly non-interacting and a strongly-interacting system. 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.
Highlights
Transport of charge, heat, and spin are often coupled in nature
Heat, and spin are often coupled in nature. Their interplay enriches the dynamical response of materials leading to coupled transport phenomena such as thermoelectricity [1] and, along conceptually similar lines, spintronics [2] and spin caloritronics [3]
We exploit the ability to compare both interaction regimes in the same structure and, by extending the accessible range of gate potentials, observe a striking reversal of the thermoelectric current directly induced by interactions
Summary
Heat, and spin are often coupled in nature. Their interplay enriches the dynamical response of materials leading to coupled transport phenomena such as thermoelectricity [1] and, along conceptually similar lines, spintronics [2] and spin caloritronics [3]. These merits have facilitated experiments on transport phenomena in strongly interacting Fermi gases, including viscous flow [15], spin diffusion [16,17], sound propagation [18,19], and heat transport in the form of second sound [20] As these experiments focused on bulk material properties, they lacked the tunability of mesoscopic systems; recent work in optically shaping bulk gases made it possible to create mesoscopic cold atom “devices” comparable to their solid-state counterparts [21,22,23,24,25,26,27,28,29]. We exploit the ability to compare both interaction regimes in the same structure and, by extending the accessible range of gate potentials, observe a striking reversal of the thermoelectric current directly induced by interactions This reversal is a novel effect in cold atoms and, to our knowledge, in strongly correlated solid materials. The initial conditions stated above correspond to the noninteracting case and are given for the unitary case in Appendix A, together with additional experimental details
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