Anomalous Suppression of Valley Splittings in Lead Salt Nanocrystals without Inversion Center

TL;DR

This paper develops an atomistic tight-binding model for PbSe and PbS nanocrystals, revealing that the absence of an inversion center significantly suppresses valley splittings, with the effect strongly dependent on nanocrystal geometry.

Contribution

It introduces a detailed atomistic model showing how nanocrystal symmetry influences valley splittings in lead salt nanocrystals.

Findings

Valley splittings are suppressed in nanocrystals lacking an inversion center.

Geometry and symmetry of nanocrystals critically affect electronic properties.

Suppression is more pronounced in T_d symmetric nanocrystals compared to O_h symmetry.

Abstract

Atomistic sp3d5s* tight-binding theory of PbSe and PbS nanocrystals is developed. It is demonstrated, that the valley splittings of confined electrons and holes strongly and peculiarly depend on the geometry of a nanocrystal. When the nanocrystal lacks a microscopic center of inversion and has T_d symmetry, the splitting is strongly suppressed as compared to the more symmetric nanocrystals with O_h symmetry, having an inversion center.