Optical switching of topological phase in a perovskite polariton lattice

Abstract

Strong light-matter interaction enriches topological photonics by dressing light with matter, which provides the possibility to realize active nonlinear topological devices with immunity to defects. Topological exciton polaritons—half-light, half-matter quasiparticles with giant optical nonlinearity—represent a unique platform for active topological photonics. Previous demonstrations of exciton polariton topological insulators demand cryogenic temperatures, and their topological properties are usually fixed. Here, we experimentally demonstrate a room temperature exciton polariton topological insulator in a perovskite zigzag lattice. Polarization serves as a degree of freedom to switch between distinct topological phases, and the topologically nontrivial polariton edge states persist in the presence of onsite energy perturbations, showing strong immunity to disorder. We further demonstrate exciton polariton condensation into the topological edge states under optical pumping. These results provide an ideal platform for realizing active topological polaritonic devices working at ambient conditions, which can find important applications in topological lasers, optical modulation, and switching.

Direct measurement of a non-Hermitian topological invariant in a hybrid light-matter system

“…We model the cavity photon by extending the Hermitian Hamiltonian ( 48 , 49 ) to properly account for the losses where ϕ is the in-plane propagation angle, is the mean complex energy of the cavity photon, is a function related to the effective mass (real part) and the momentum-dependent loss rates (imaginary part), describes the complex energy splitting due to X - Y splitting, and describes transverse-electric transverse-magnetic (TE-TM) splitting. The X - Y splitting can arise from the birefringence in the cavity medium ( 48 , 49 ), for example, due to the anisotropic orthorhombic crystal structure of perovskites at room temperature ( 33 , 50 ), which leads to different cavity lengths for the ordinary and extraordinary waves and results in the splitting of both energies and linewidths at normal incidence ( k = 0). The TE-TM splitting naturally arises from the polarization-dependent reflectivity of the dielectric mirrors at oblique angles, inducing an effective spin-orbit coupling ( 48 – 50 ) that increases with the angle of incidence (or k ).…”

“…It is formed by sandwiching a ~142-nm-thick CsPbBr 3 perovskite crystal between two SiO 2 /Ta 2 O 5 DBRs, as detailed in Materials and Methods. The crystal is optically anisotropic because of its orthorhombic symmetry ( 33 , 52 , 53 ), which leads to X - Y splitting of the exciton-polariton states ( 33 , 50 ). The exciton polaritons are excited by an off-resonant laser with the photon energy far above the perovskite exciton energy.…”

Electrical Switching of Optical Gain in Perovskite Semiconductor Nanocrystals

“…Lead halides of perovskite lattices have emerged as a family of semiconductors promising for optoelectronic applications. − Nanocrystal structures can further improve the strength of light–matter interaction benefiting from the quantum confinement effect. − Highly efficient light absorption and emission make perovskite semiconductor nanocrystals ideal gain media for laser demonstration. ,− Nevertheless, the inherent degeneracies of band-edge states require a relatively high pump threshold of more than one exciton per nanocrystal to achieve the population inversion to support optical gain in these nanocrystals. − …”

Kagome Flatbands for Coherent Exciton-Polariton Lasing

“…The unique part-light, part-matter composition of these polaritons facilitated the observation of polariton condensates that emit coherent laser light . Using a variety of confinement techniques, lattice potential environments can be designed for exciton-polaritons allowing one to study the emergence of polaritonic band structures , which were subsequently even driven into a topologically nontrivial regime. , Recently, advances in the fabrication of polariton lattices operating at room temperature were made leading to successful realizations of a wide variety of polariton lattices employing perovskite , and organic − emitters. In addition, optically induced polariton potentials have been demonstrated to have reached a maturity that allows for sophisticated polariton lattice formation. , Flatbands have been realized in one-dimensional , as well as two-dimensional − polaritonic lattices as well, where in particular the Lieb lattice has facilitated precise control over the flatness of the flatbands .…”