Exciton-polaritons in CsPbBr$_3$ crystals revealed by optical reflectivity in high magnetic fields and two-photon spectroscopy

TL;DR

This study investigates exciton-polaritons in CsPbBr$_3$ crystals using high magnetic field reflectivity and two-photon spectroscopy, providing detailed quantitative parameters of excitonic states and their interactions.

Contribution

It offers the first comprehensive quantitative analysis of exciton-polaritons in CsPbBr$_3$ crystals, including exciton binding energy, oscillator strength, and Landé factor, within a hydrogen-like model.

Findings

Exciton binding energy of 32.5 meV

Oscillator strength with 5.3 meV splitting

Exciton Landé factor of +2.35

Abstract

Cesium lead bromide (CsPbBr$_3$) is a representative material of the emerging class of lead halide perovskite semiconductors that possess remarkable optoelectronic properties. Its optical properties in the vicinity of the band gap energy are greatly contributed by excitons, which form exciton-polaritons due to strong light-matter interactions. We examine exciton-polaritons in solution-grown CsPbBr$_3$ crystals by means of circularly-polarized reflection spectroscopy measured in high magnetic fields up to 60 T. The excited 2P exciton state is measured by two-photon absorption. Comprehensive modeling and analysis provides detailed quantitative information about the exciton-polariton parameters: exciton binding energy of 32.5 meV, oscillator strength characterized by longitudinal-tranverse splitting of 5.3 meV, damping of 6.7 meV, reduced exciton mass of $0.18 m_0$, exciton diamagnetic shift of 1.6 $\mu$eV/T$^2$, and exciton Land\'e factor $g_X=+2.35$. We show that the exciton states can be well described within a hydrogen-like model with an effective dielectric constant of 8.7. From the measured exciton longitudinal-transverse splitting we evaluate the Kane energy of $E_p=15$ eV, which is in reasonable agreement with values of $11.8-12.5$ eV derived from the carrier effective masses.