Abstract
Quantum impurities give rise to rich physical phenomena, with some exhibiting critical behavior described by conformal field theories (CFTs) in the low-energy limit. In parallel, party-time (PT) symmetric non-Hermitian systems host exceptional points (EPs) at criticality, leading to exotic features governed by nonunitary CFTs. Here, we establish a connection between non-Hermitian impurities and CFTs by demonstrating that the critical properties of a (1 + 1)-dimensional free-fermion chain with central charge c = 1 can be drastically altered by the presence of a local non-Hermitian impurity. Through a systematic analysis of entanglement/R & eacute;nyi entropy, the finite-size scaling of the many-body spectrum, and fidelity susceptibility, we identify that this impurity-induced non-Hermitian criticality is characterized by a nonunitary CFT with central charge c = -2. Furthermore, we find that these nonunitary critical properties exhibit strong sensitivity to boundary conditions.