Light-Driven Bound State of Interacting Impurities in a Dirac-Like Bath

TL;DR

This paper introduces a microscopic framework for understanding how periodic driving in quantum impurity systems can lead to emergent non-Hermitian phenomena, such as exceptional points, with measurable effects on the density of states.

Contribution

It develops an auxiliary-fermion approach capturing spin-orbit effects and predicts symmetry-protected gain-loss channels and eigenvector non-orthogonality effects near exceptional points.

Findings

Eigenvector non-orthogonality enhances impurity density of states.

Exceptional points arise dynamically from hybridization, not inserted artificially.

Density of states enhancement signals the presence of exceptional points.

Abstract

Strongly correlated quantum impurities under periodic driving can exhibit emergent non-Hermitian phenomena, yet a microscopic understanding has been lacking. We introduce an auxiliary-fermion framework that captures the bath's spin-orbit and angular-momentum structure and generates an effective low-energy theory with symmetry-protected spin-selective gain-loss channels. Exceptional points (EPs) arise dynamically from hybridization, without inserting non-Hermitian terms by hand, while causality is preserved via sign-reversing contributions. Near EPs, eigenvector non-orthogonality strongly enhances the impurity density of states, boosting the Kondo scale according to the condition number of the effective Hamiltonian. This DOS enhancement provides a directly measurable signature of EPs in impurity systems when spin-flip processes are induced experimentally. The pseudo-Hermitian structure further enables a biorthogonal thermodynamic Bethe ansatz treatment of interactions. Our results establish a unified route by which driven environments can engineer correlated, emergent non-Hermitian impurity states, opening a new avenue to control quantum many-body systems far from equilibrium.