Tunneling Transport of Unitary Fermions across the Superfluid Transition
Authors: Del Pace G., Kwon W. J., Zaccanti M., Roati G., Scazza F.
Autors Affiliation: Department of Physics and Astronomy, University of Florence, 50019 Sesto Fiorentino, Italy
European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
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.
Journal/Review: PHYSICAL REVIEW LETTERS
Volume: 126 (5) Pages from: 055301-1 to: 055301-7
More Information: We are indebted to Jean-Philippe Brantut, Eugene Demler, Tilman Enss, Carlos Sa De Melo, Verdiana Piselli, Giancarlo Strinati, Wilhelm Zwerger, and Massimo Inguscio for inspiring discussions. We thank Bernhard Frank for providing us with finite-temperature Luttinger-Ward calculations of the condensed fraction of the homogeneous unitary Fermi gas, Michele Pini for providing us with self-consistent calculations of the critical temperature, and Riccardo Panza for assistance during the construction of the experimental setup. This work was supported by the European Research Council under GA No. 307032, Ente Cassa di Risparmio di Firenze Project No. 2016.0770, the Italian MIUR under the PRIN2017 project CEnTraL, and EU´s Horizon 2020 research and innovation programme under the Qombs project FET Flagship on Quantum Technologies GA No. 820419, and Marie Sklodowska-Curie GAs No. 705269 and No. 843303.KeyWords: Fermi gases, Fermionic condensates, Josephson effect, Quantum transport, Quasiparticles & collective excitations, Superfluidity, Transport phenomena, Tunnel junctionsDOI: 10.1103/PhysRevLett.126.055301