We investigate the transport of a Fermi gas with unitarity-limited interactions across the superfluid phase transition, probing its response to a direct current (dc) drive through a tunnel junction. As the superfluid critical temperature is crossed from below, we observe the evolution from a highly nonlinear to an Ohmic conduction characteristic, associated with the critical breakdown of the Josephson dc current induced by pair condensate depletion. Moreover, we reveal a large and dominant anomalous contribution to resistive currents, which reaches its maximum at the lowest attained temperature, fostered by the tunnel coupling between the condensate and phononic Bogoliubov-Anderson excitations. Increasing the temperature, while the zeroing of supercurrents marks the transition to the normal phase, the conductance drops considerably but remains much larger than that of a normal, uncorrelated Fermi gas tunneling through the same junction. We attribute such enhanced transport to incoherent tunneling of sound modes, which remain weakly damped in the collisional hydrodynamic fluid of unpaired fermions at unitarity.

Tunneling Transport of Unitary Fermions across the Superfluid Transition / G. Del Pace, W.J. Kwon, M. Zaccanti, G. Roati, F. Scazza. - In: PHYSICAL REVIEW LETTERS. - ISSN 0031-9007. - 126:5(2021 Feb 04), pp. 055301.1-055301.7. [10.1103/PhysRevLett.126.055301]

Tunneling Transport of Unitary Fermions across the Superfluid Transition

W.J. Kwon
Secondo
;
2021

Abstract

We investigate the transport of a Fermi gas with unitarity-limited interactions across the superfluid phase transition, probing its response to a direct current (dc) drive through a tunnel junction. As the superfluid critical temperature is crossed from below, we observe the evolution from a highly nonlinear to an Ohmic conduction characteristic, associated with the critical breakdown of the Josephson dc current induced by pair condensate depletion. Moreover, we reveal a large and dominant anomalous contribution to resistive currents, which reaches its maximum at the lowest attained temperature, fostered by the tunnel coupling between the condensate and phononic Bogoliubov-Anderson excitations. Increasing the temperature, while the zeroing of supercurrents marks the transition to the normal phase, the conductance drops considerably but remains much larger than that of a normal, uncorrelated Fermi gas tunneling through the same junction. We attribute such enhanced transport to incoherent tunneling of sound modes, which remain weakly damped in the collisional hydrodynamic fluid of unpaired fermions at unitarity.
Settore PHYS-03/A - Fisica sperimentale della materia e applicazioni
   Quantum simulation and entanglement engineering in quantum cascade laser frequency combs
   Qombs
   European Commission
   Horizon 2020 Framework Programme
   820419

   Quantum simulation of two-dimensional fermionic systems
   QUFERM2D
   European Commission
   SEVENTH FRAMEWORK PROGRAMME
   307032

   Strongly correlated ultracold fermions in two-dimensional tailored optical potentials: pairing, superfluidity and disorder
   SCOUTFermi2D
   European Commission
   Horizon 2020 Framework Programme
   705269
4-feb-2021
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/1105149
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