Dissipative-interaction-induced polaron-molecule transition in three-dimensional Fermi polarons

The non-Hermitian interaction in many-body systems may lead to novel phenomena. We study an impurity immersed in three-dimensional ideal Fermi gases, with a complex-valued contact interaction between the fermions and impurity that arise from two-body dissipation. Generalizing the unified variational approach to the non-Hermitian case, we study the effects of the dissipative attraction on the polaronic and molecular states of the impurity for different mass ratios. We find that the dissipation attraction can induce polaron-molecule transition despite the transition being absent in the Hermitian case, which is demonstrated to be a first-order phase transition between different total momenta. In addition, we show that the non-Hermitian attraction leads to significant decay of the polaronic and molecular states; however, increasing the mass ratio between the impurity and majority fermions will help suppress the decay. Our results illustrate the applicability of the unified variational approach in non-Hermitian Fermi polaron systems and the method may be extended to include higher-order particle-hole excitations and to study other types of bound states.