Stoner Instability in a Strongly Repulsive Fermi Gas

POSTER

Abstract

We study the existence of itinerant ferromagtism using a ultracold Fermi gas with short range repulsion in a harmonic trap. A degenerate Fermi gas is rapidly quenched into the regime of strong effective repulsion near a Feshbach resonance. The spin fluctuations are monitored using speckle imaging and, contrary to several theoretical predictions, the samples remain in the paramagnetic phase for arbitrarily large scattering length. We also observe a rapid decay into bound pairs over times on the order of $10\hbar/E_{F}$ in a wide range of interaction strengths, which is intrinsic by the nature of Feshbach resonance and preventing the study of equilibrium phases of strongly repulsive fermions. Our work suggests that a Fermi gas with strong short-range repulsive interactions does not undergo a ferromagnetic phase transition.

*This work was supported by NSF and ONR, AFOSR MURI, and under ARO from the DARPA Optical Lattice Emulator program.

Authors

  • Wujie Huang

    • Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology

  • Christian Sanner

    • Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology

  • Edward Su

    • Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology

  • Aviv Keshet

    • Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology

  • Jonathon Gillen

    • Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology

  • Wolfgang Ketterle

    • Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology