Activating non-Hermitian skin modes by parity-time symmetry breaking
Zhoutao Lei, Ching Hua Lee, Linhu Li
Abstract
Abstract Parity-time ( $${{{{{{{\mathcal{PT}}}}}}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>PT</mml:mi></mml:math> ) symmetry is a cornerstone of non-Hermitian physics as it ensures real energies for stable experimental realization of non-Hermitian phenomena. In this work, we propose $${{{{{{{\mathcal{PT}}}}}}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>PT</mml:mi></mml:math> symmetry as a paradigm for designing rich families of higher-dimensional non-Hermitian states with unique bulk, surface, hinge or corner dynamics. Through systematically breaking or restoring $${{{{{{{\mathcal{PT}}}}}}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>PT</mml:mi></mml:math> symmetry in different sectors of a system, we can selectively activate or manipulate the non-Hermitian skin effect (NHSE) in both the bulk and topological boundary states. Some fascinating phenomena include the directional toggling of the NHSE, and the flow of boundary states without chiral or dynamical pumping, developed from selective boundary NHSE. Our results extend richly into 3D or higher, with more sophisticated interplay with selective bulk and boundary NHSE and charge-parity ( $${{{{{{{\mathcal{CP}}}}}}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>CP</mml:mi></mml:math> ) symmetry. Based on non-interacting lattices, $${{{{{{{\mathcal{PT}}}}}}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>PT</mml:mi></mml:math> -activated NHSEs can be observed in various optical, photonic, electric and quantum platforms that admit gain/loss and non-reciprocity.