Non-Hermitian trapping of Dirac exciton-polariton condensates in a perovskite metasurface.

Abstract

Massless Dirac particles avoid trapping because of their exceptional tunneling properties manifested in the so-called Klein paradox. This conclusion stems from the conservative treatment, but so far, it has not been extended to a non-Hermitian framework. Recently, driven-dissipative bosonic condensation of exciton-polaritons featuring Dirac dispersion was demonstrated in metasurface waveguides-a platform rich in non-Hermitian effects. Here, we report an experimental observation of spatial binding and energy quantization of Dirac polaritons in a halide perovskite metasurface. A combination of spatially profiled nonresonant optical excitation and exciton-polariton interaction forms an effective non-Hermitian complex potential responsible for the observed effect. In the case of tightly focused pump spots spanning from 9 to 17 micrometers, several bound states simultaneously achieve macroscopic occupation, constituting a multimode bosonic condensation of exciton-polaritons. Our theoretical analysis based on the driven-dissipative extension of the Dirac equation reveals a non-Hermitian confinement mechanism that bypasses the Klein paradox. Unlike previous observations limited to massive Dirac gaps, the non-Hermitian trap confines particles even in a gapless spectrum on both sides of the Dirac point.