Binding energy of polaronic trions and biexcitons in CsPbBr$_3$ nanocrystals

TL;DR

This study investigates how polaron formation influences the binding energies of excitons, trions, and biexcitons in CsPbBr$_3$ nanocrystals, revealing good agreement for trions but unexplained high biexciton energies.

Contribution

It introduces a detailed theoretical analysis of polaronic effects on excitonic complexes in CsPbBr$_3$ nanocrystals, highlighting the limitations of current models for biexcitons.

Findings

Trion binding energies match experimental data.

Biexciton energies are not fully explained by polaronic or dielectric effects.

Biexcitons may polarize the lattice differently, affecting their binding energies.

Abstract

The effect of polaron formation on the ground state of excitons, trions and biexcitons confined in CsPbBr$_3$ nanocrystals is studied in the framework of effective mass Hamiltonians, using a Haken-like (Bajaj) potential for carrier-phonon coupling. The binding energy of trions agrees well with that observed in experiments, with position-dependent dielectric screening playing a significant role. For biexcitons, however, neither polaronic effects, nor dielectric confinement, nor electronic correlations -- here accounted for with a variational Quantum Monte Carlo method -- suffice to explain the large binding energies reported by single nanocrystal spectroscopy experiments. This result reinforces the hypothesis that biexcitons polarize the perovskite lattice differently from excitons and trions.