# Spectral singularity enhances transverse spin

## TL;DR

This paper investigates how spectral singularities in a $ ext{PT}$-symmetric waveguide can dramatically amplify the transverse spin and spin momentum, which are usually very small and difficult to detect.

## Contribution

It demonstrates that spectral singularities can significantly enhance the transverse spin and spin momentum in a gain-loss balanced waveguide, providing new insights into their control and measurement.

## Key findings

- Spectral singularities lead to infinite scattering amplitudes.
- Near spectral singularities, transverse spin and spin momentum are dramatically enhanced.
- Experimental observations of tiny spin quantities can be amplified using this method.

## Abstract

We study the transverse spin and the Belinfante spin momentum in a gain-loss balanced waveguide, known to be one of the first and most studied examples of $\mathcal{PT}$-symmetric systems. Such a guide supports the spectral singularities leading to infinite scattering amplitudes for both reflection and transmission. We show that near the spectral singularity there can be dramatic enhancement of the transverse spin and the transverse spin momentum. Note that these exotic spin and spin momentum have recently been observed experimentally despite having tiny magnitudes, making it worthy to explore ways and means to enhance these fundamentally important elusive quantities.