# Helical resonant transport and purified amplification at an exceptional point

## TL;DR

This paper explores a non-Hermitian SSH model embedded in a 2D lattice tube, demonstrating chiral helical transport and amplification at an exceptional point, with potential applications in all-optical devices.

## Contribution

It introduces a novel application of a parity-time symmetric non-Hermitian SSH model for controlled helical transport and amplification without magnetic fields.

## Key findings

- Perfect transmission with same helicity incidence
- Amplified transmission with opposite helicity incidence
- Helical amplification triggered by arbitrary excitation

## Abstract

We propose an application of a parity-time symmetric non-Hermitian Su-Schrieffer-Heeger (SSH) model by embedded it in a two-dimensional square lattice tube. The coalescence state at the exceptional point of non-Hermitian SSH model is chiral and selectively controls helical transport and amplification. Two typical helicity-dependent scattering dynamics are observed. If the incidence has an identical helicity with the embedded non-Hermitian SSH model, we observe a perfect transmission without reflection. However, if the incidence has an opposite helicity with the embedded non-Hermitian SSH model, except for a full transmission, we observe an amplified transmission with different helicity from the incidence; but the amplified reflection has identical helicity with the incidence. These intriguing features are completely unexpected in Hermitian system. Moreover, the helical amplification at high efficiency can be triggered by an arbitrary excitation. The different dynamics between incidences with opposite helicities are results of unidirectional tunneling, which is revealed to be capable of realizing without introducing magnetic field. Our findings open a direction in all-optical device and provide perspectives in non-Hermitian transport.