Phase transitions and spectral singularities in a class of one-dimensional parity-time-symmetric complex potentials

TL;DR

This paper explores phase transitions and spectral singularities in a class of one-dimensional parity-time-symmetric complex potentials, revealing two distinct transition types and their implications for wave scattering and device design.

Contribution

It introduces a detailed analysis of phase transitions and spectral singularities in PT-symmetric potentials, including exact bound states and a universal relationship for spectral singularities.

Findings

Identification of two types of phase transitions in PT-symmetric potentials

Establishment of a universal relationship governing spectral singularities

Construction of exact bound state solutions under specific conditions

Abstract

We investigate a two-parametric family of one-dimensional non-Hermitian complex potentials with parity-time ($\mathcal{PT}$) symmetry. We find that there exist two distinct types of phase transitions, from an unbroken phase (characterized by a real spectrum) to a broken phase (where the spectrum becomes complex). The first type involves the emergence of a pair of complex eigenvalues bifurcating from the continuous spectrum. The second type is associated with the collision of such pairs at the bottom of the continuous spectrum. The first transition type is closely related to spectral singularities (SSs), at which point the transmission and reflection coefficients are divergent simultaneously. The second is associated with the emergence of bound states. In particular, under specific parameter conditions, we construct an exact bound state solution. By systematically exploring the parameter space, we establish a universal relationship governing the number of SSs in these potentials. These findings provide a fundamental theoretical framework for manipulating wave scattering in non-Hermitian systems, offering promising implications for designing advanced optical and quantum devices.