Non-Hermitian Ferromagnetism in an Ultracold Fermi Gas

Hiroyuki Tajima; Kei Iida

doi:10.7566/jpsj.90.024004

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arXiv · 2004.05577

Non-Hermitian Ferromagnetism in an Ultracold Fermi Gas

Hiroyuki Tajima·Kei Iida

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Abstract

We develop a non-Hermitian effective theory for a repulsively interacting Fermi gas in the excited branch. The on-shell $T$-matrix is employed as a complex-valued interaction term, which describes a repulsive interaction between atoms in the excited branch and a two-body inelastic decay to the attractive branch. To see the feature of this model, we have addressed, in the weak coupling regime, the excitation properties of a repulsive Fermi polaron as well as the time-dependent number density. The analytic expressions obtained for these quantities qualitatively show a good agreement with recent experiments. By calculating the dynamical transverse spin susceptibility in the random phase approximation, we show that a ferromagnetic system with nonzero polarization undergoes a dynamical instability and tends towards a heterogeneous phase.

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BibTeX RIS

Hiroyuki Tajima, Kei Iida. 2020-04-12. Non-Hermitian Ferromagnetism in an Ultracold Fermi Gas. https://doi.org/10.7566/jpsj.90.024004

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