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Despite its seeming simplicity, a Fermi gas of ultracold atoms with strong repulsive interactions exhibits a complex behavior, resulting from the competing action of two distinct instabilities — ferromagnetism and pairing. The breakdown of the repulsive Fermi liquid state, 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)], leading also to the discovery of an emergent metastable microemulsion state of anticorrelated fermions and pairs. Here, we investigate the properties of such correlated many-body regime by preparing a strongly repulsive Fermi gas, and studying the evolution of kinetic and release energies, of the spectral response and coherence of the unpaired fermionic population, and of its spin-density noise correlations. All our observations consistently point to a low-temperature heterogeneous phase, where paired and unpaired fermions macroscopically coexist while exhibiting microscale inhomogeneity. Our findings open the exploration of quantum emulsions and possibly of inhomogeneous superfluid regimes. F. Scazza et al. |
Fermions with tunable interactions... In the lithium lab we produce ultracold Fermi gases of 6Li to explore out-of-equilibrium dynamics and transport phenomena in strongly correlated fermionic matter. Atoms are confined into light-imprinted potential structures, simulating the motion of electrons in solid state devices. Our main goal is the study of two-dimensional strongly correlated phases, such as superfluidity across the BCS-BEC crossover and its robustness to disorder.