Scientific Results

Exploring emergent heterogeneous phases in strongly repulsive Fermi gases

Year: 2020

Authors: Scazza F., Valtolina G., Amico A., Tavares PES, Inguscio M., Ketterle W., Roati G., Zaccanti M.

Autors Affiliation: CNR, INO, I-50019 Sesto Fiorentino, Italy

Univ Firenze, European Lab Nonlinear Spect LENS, I-50019 Sesto Fiorentino, Italy

Univ Colorado, JILA, Boulder, CO 80309 USA

Univ Firenze, Dipartimento Fis & Astron, I-50019 Sesto Fiorentino, Italy

Univ Fed Minas Gerais, Dept Fis, BR-31270901 Belo Horizonte, MG, Brazil

Univ Rome, Dept Engn, Campus Biomed, I-00128 Rome, Italy

MIT, Dept Phys, Harvard Ctr Ultracold Atoms, Cambridge, MA 02139 USA

MIT, Res Lab Elect, Cambridge, MA 02139 USA

Abstract: Recent experiments have revitalized the interest in a Fermi gas of ultracold atoms with strong repulsive interactions. In spite of its seeming simplicity, this system exhibits a complex behavior, resulting from the competing action of two distinct instabilities: ferromagnetism, which promotes spin anticorrelations and domain formation; and pairing, which renders the repulsive fermionic atoms unstable toward forming weakly bound bosonic molecules. The breakdown of the homogeneous repulsive Fermi liquid arising from such concurrent mechanisms has been recently observed in real time through pump-probe spectroscopic techniques [A. Amico et al., Phys. Rev. Lett. 121. 253602 (2018)]. These studies also lead to the discovery of an emergent metastable many-body state, an unpredicted quantum emulsion of anticorrelated fermions and pairs. Here, we investigate in detail the properties of such an exotic regime by studying the evolution of kinetic and release energies, the spectral response and coherence of the unpaired fermionic population, and its spin-density noise correlations. All our observations consistently point to a low-temperature heterogeneous phase, where paired and unpaired fermions macroscopically coexist while featuring microscale phase separation. Our findings open appealing avenues for the exploration of quantum emulsions and also possibly of inhomogeneous superfluid regimes, where pair condensation may coexist with magnetic order

Journal/Review: PHYSICAL REVIEW A

Volume: 101      Pages from: 013603-1  to: 013603-12

KeyWords: ULTRACOLD GASES, FERMI GASES, FERROMAGNETISM, DOMAIN FORMATION, HETEROGENEOUS PHASE
DOI: 10.1103/PhysRevA.101.013603