Generalized Surface Polaritons and their quantum spin Hall effect

TL;DR

This paper uncovers conditions for lossless surface polaritons at gain-loss interfaces, revealing a new polariton type with spin Hall effects and topological properties, advancing nanophotonics and non-Hermitian optics.

Contribution

It introduces a new class of lossless surface polaritons induced by permittivity sign changes, with topological and spin Hall effects, expanding understanding of non-Hermitian surface waves.

Findings

Discovered lossless surface polaritons at gain-loss interfaces.

Identified spin Hall effect due to spin-momentum locking.

Quantized spin Hall coefficient with topological implications.

Abstract

Surface polaritons, e.g., surface plasmon polaritons, are invaluable tools in nanophotonics. However, considerable plasmon loss narrows the application regime of plasmonic devices. Here we reveal some general conditions for lossless surface polaritons to emerge at the interface of a gain and a loss media. The gain medium does not only compensate the energy loss, but also modifies surface wave oscillation mechanisms. A new type of surface polaritons induced by the sign switch of the imaginary part of the permittivity across the interface is discovered. The surface polaritons exhibit spin Hall effect due to spin-momentum locking and unique Berry phase. The spin Hall coefficient changes the sign across the parity-time symmetric limit and becomes quantized for perfect metal-dielectric interface and for dielectric-dielectric interface with very large permittivity contrast, carrying opposite topological numbers. Our study opens a new direction for manipulating light with surface polaritons in non-Hermitian optical systems.