Repulsive Fermi Polarons in a Resonant Mass-Balanced Fermi Mixture
February 16th, 2017 FRANCESCO SCAZZA INO-CNR and LENS

Understanding the properties of an impurity immersed in a degenerate quantum medium represents a fundamental problem in many-body physics. In particular, the Fermi polaron problem and the associated repulsive quasiparticle are centrally important for describing and realizing many-body states arising from repulsive interactions. We employ radio-frequency spectroscopy to investigate spin mixtures of ultracold Li-6 atoms with tunable polarization in the vicinity of a broad Feshbach resonance. At high spin-imbalance, we report on the observation of well-defined coherent quasiparticles up to unitarity-limited interactions [1]. We characterize the many-body system by extracting the key elastic and inelastic properties of repulsive Fermi polarons: the energy E+, the effective mass m*, the residue Z and the decay rate Γ. Above a critical interaction, we find E+ to exceed the Fermi energy of the bath, while m* diverges and even turns negative, revealing an energetic and thermodynamic instability of the repulsive Fermi liquid. Motivated by these findings, in ongoing experiments we investigate the evolution of the interaction energy and of spin correlations in a balanced spin mixture after a rapid radio-frequency transfer to the strongly repulsive regime.

Seminar, February 16, 2017, 15:00. Seminar Room

Hosted by Prof. Maciej Lewenstein