Resonant-amplified and invisible Bragg scattering based on spin coalescing modes

TL;DR

This paper explores how exceptional points in complex fields can create invisible and amplifying Bragg scattering in engineered superlattices, revealing unique EP dynamics and potential for resonant amplification.

Contribution

It introduces a novel mechanism using exceptional point modes to achieve resonant amplification and invisibility in Bragg scattering within superlattices.

Findings

Resonant amplification observed in numerical simulations.

Invisibility of Bragg scattering demonstrated.

EP modes support mutual stimulation and unique dynamics.

Abstract

Unlike a real magnetic field, which separates the energy levels of particle with opposite spin polarization, a complex field can lead to a special kind of spectral degeneracy, known as exceptional point (EP), at which two spin eigenmodes coalesce. It allows an EP impurity to be an invisible scattering center for a fermion with the resonant spin polarization, but an amplifying emitter for opposite polarization. We show that a pair of conjugate EP modes supports resonant mutual stimulation, acting as a resonant amplifier based on the underlying mechanism of positive-feedback loop. Together with other Hermitian eigenmodes, a fermion with EP polarization exhibits some exclusive dynamics, referred to as EP dynamics. We construct several typical superlattices, which are built up by embedding EP-impurity arrays in a Hermitian two-dimensional square lattice. Numerical simulations are performed to demonstrate resonant amplification and invisibility of Bragg scattering.