Halide perovskites enable polaritonic XY spin Hamiltonian at room temperature.

Exciton polaritons, the part-light and part-matter quasiparticles in semiconductor optical cavities, are promising for exploring Bose-Einstein condensation, non-equilibrium many-body physics and analogue simulation at elevated temperatures. However, a room-temperature polaritonic platform on par with the GaAs quantum wells grown by molecular beam epitaxy at low temperatures remains elusive. The operation of such a platform calls for long-lifetime, strongly interacting excitons in a stringent material system with large yet nanoscale-thin geometry and homogeneous properties. Here, we address this challenge by adopting a method based on the solution synthesis of excitonic halide perovskites grown under nanoconfinement. Such nanoconfinement growth facilitates the synthesis of smooth and homogeneous single-crystalline large crystals enabling the demonstration of XY Hamiltonian lattices with sizes up to 10 × 10. With this demonstration, we further establish perovskites as a promising platform for room temperature polaritonic physics and pave the way for the realization of robust mode-disorder-free polaritonic devices at room temperature.

Room-temperature polariton quantum fluids in halide perovskites.

Quantum fluids exhibit quantum mechanical effects at the macroscopic level, which contrast strongly with classical fluids. Gain-dissipative solid-state exciton-polaritons systems are promising emulation platforms for complex quantum fluid studies at elevated temperatures. Recently, halide perovskite polariton systems have emerged as materials with distinctive advantages over other room-temperature systems for future studies of topological physics, non-Abelian gauge fields, and spin-orbit interactions. However, the demonstration of nonlinear quantum hydrodynamics, such as superfluidity and Cerenkov flow, which is a consequence of the renormalized elementary excitation spectrum, remains elusive in halide perovskites. Here, using homogenous halide perovskites single crystals, we report, in both one- and two-dimensional cases, the complete set of quantum fluid phase transitions from normal classical fluids to scatterless polariton superfluids and supersonic fluids-all at room temperature, clear consequences of the Landau criterion. Specifically, the supersonic Cerenkov wave pattern was observed at room temperature. The experimental results are also in quantitative agreement with theoretical predictions from the dissipative Gross-Pitaevskii equation. Our results set the stage for exploring the rich non-equilibrium quantum fluid many-body physics at room temperature and also pave the way for important polaritonic device applications.

Directional Light Emission from Layered Metal Halide Perovskite Crystals.

Metal halide perovskites are being increasingly explored for use in light-emitting diodes (LEDs), with achievements in efficiency and brightness charted across the spectrum. One path to further boosting the fraction of useful photons generated by injected electrical charges will be to tailor the emission patterns of devices. Here we investigate directional emission from layered metal halide perovskites. We quantify the proportion of in-plane versus out-of-plane transition dipole components for a suite of layered perovskites. We find that certain perovskite single crystals have highly anisotropic emissions and up to 90% of their transition dipole in-plane. For thin films, emission anisotropy increases as the nominal layer thickness decreases and is generally greater with butylammonium cations than with phenethylammonium cations. Numerical simulations reveal that anisotropic emission from layered perovskites in thin-film LEDs may lead to external quantum efficiencies of 45%, an absolute gain of 13% over equivalent films with isotropic emitters.