Anomalous circular polarization of magneto-photoluminescence from individual CdSe nanocrystals

TL;DR

This study investigates the magneto-photoluminescence behavior of individual CdSe nanocrystals at low temperatures, revealing an unusual circular polarization phenomenon linked to exciton level mixing caused by anisotropic exchange interactions.

Contribution

It uncovers an anomalous circular polarization in magneto-PL from CdSe nanocrystals with large fine structure splitting, highlighting the role of anisotropic exchange interactions.

Findings

Nanocrystals with small splitting show conventional Zeeman doublets.

Large splitting nanocrystals exhibit anomalous polarization behavior.

Strong anisotropic exchange causes mixing of exciton levels.

Abstract

We study the low-temperature magneto-photoluminescence (PL) from individual CdSe nanocrystals. Nanocrystals having a small "bright" exciton fine structure splitting ($<$0.5 meV) exhibit a conventional left- and right-circularly polarized Zeeman PL doublet in applied magnetic fields. In contrast, nanocrystals with large fine structure splitting ($>$1 meV) show an anomalous magneto-PL polarization, wherein the lower-energy peak becomes circularly polarized with increasing field, while the higher-energy peak remains linearly polarized. This unusual behavior arises from strong mixing between the absorbing and emitting bright exciton levels due to strong anisotropic exchange interactions.