title: Observation of Fermi polarons in a tunable Fermi liquid of ultracold atoms.
abstract: We have observed Fermi polarons, dressed spin-down impurities in a spin-up Fermi sea of ultracold atoms. The polaron manifests itself as a narrow peak in the impurities' rf spectrum that emerges from a broad incoherent background. We determine the polaron energy and the quasiparticle residue for various interaction strengths around a Feshbach resonance. At a critical interaction, we observe the transition from polaronic to molecular binding. Here, the imbalanced Fermi liquid undergoes a phase transition into a Bose liquid, coexisting with a Fermi sea.
authors: Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors: André
authors: A
authors: Schirotzek
authors: Cheng-Hsun
authors: CH
authors: Wu
authors: Ariel
authors: A
authors: Sommer
authors: Martin W
authors: MW
authors: Zwierlein