Repulsive Fermi polarons with negative effective mass

Abstract

Recent LENS experiment on a 3D Fermi gas has reported a negative effective mass ($m^{\ast }<0$) of Fermi polarons in the strongly repulsive regime. There naturally arise a question whether the negative $m^{\ast }$ is a precursor of the instability towards phase separation (or itinerant ferromagnetism). In this work, we make use of the exact solutions to study the ground state and excitation properties of repulsive Fermi polarons in 1D, which can also exhibit a negative $m^{\ast }$ in the super Tonks-Girardeau regime. By analyzing the total spin, quasi-momentum distribution and pair correlations, we conclude that the negative $m^{\ast }$ is irrelevant to the instability towards ferromagnetism or phase separation, but rather an intrinsic feature of collective excitations for fermions in the strongly repulsive regime. Surprisingly, for large and negative $m^{\ast }$, such excitation is accompanied with a spin density modulation when the majority fermions move closer to the impurity rather than being repelled far away, contrary to the picture of phase separation. These results suggest an alternative interpretation of negative $m^{\ast }$ as observed in recent LENS experiment.

6 pages, 3 figures

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Cited by in corpus (8)

• Repulsive Fermi Polarons and Their Induced Interactions in Binary Mixtures of Ultracold Atoms
• High-precision numerical solution of the Fermi polaron problem and large-order behavior of its diagrammatic series
• Probing Ferromagnetic Order in Few-Fermion Correlated Spin-Flip Dynamics
• Interplay of phase separation and itinerant magnetism for correlated few fermions in a double-well
• Polaronic neutron in dilute alpha matter: A $p$-wave Bose polaron
• Impurity in a zero-temperature three-dimensional Fermi gas
• Effective Fermion Mass in Relativistic and Non-Relativistic Systems
• Quench dynamics and quantum flutter properties of one-dimensional attractive single-spin flipped Fermi gases