Erlangen 2018 – wissenschaftliches Programm

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Q: Fachverband Quantenoptik und Photonik

Q 25: Quantum Gases (Fermions) I

Q 25.5: Vortrag

Montag, 5. März 2018, 17:15–17:30, K 1.022

Violation of the Wiedemann-Franz law in a unitary Fermi gas — •Samuel Häusler, Dominik Husmann, Martin Lebrat, Philipp Fabritius, Laura Corman, Jean-Philippe Brantut, and Tilman Esslinger — Institute for Quantum Electronics, ETH Zurich, 8093 Zürich, Switzerland

In materials heat and particle transport are often coupled, leading to thermoelectric effects. A temperature gradient may cause particle transport (Seebeck effect) and a variation in chemical potential can induce heat currents (Peltier effect). These phenomena are suited to probe the fundamental excitations that are challenging to identify in strongly correlated matter.

To study these phenomena, we prepare a system consisting of two reservoirs of fermionic lithium atoms at unitarity close to the superfluid transition. After heating one of the reservoirs they may exchange particles and heat through a quantum point contact. We observe a violent initial particle current from cold to hot that brings the system to a non-equilibrium steady state where currents vanish in the presence of finite temperature difference and chemical potential bias. The steady state reveals a finite particle and suppressed thermal conductance strongly violating the Wiedemann-Franz law, which relates the two conductances by a universal number in the limit of low temperatures. This violation signals a breakdown of Fermi liquid behaviour and remains for wider channel geometries, where the system relaxes back to equilibrium. These findings are related to the celebrated fountain effect in bosonic helium II.