Anomalous Circular Polarization of Photoluminescence Spectra of Individual CdSe Nanocrystals in an Applied Magnetic Field

Abstract

We study the low-temperature magnetophotoluminescence from individual CdSe nanocrystals. Nanocrystals having a small “bright” exciton fine structure splitting (${\Delta }_{XY}<0.5\mathrm{meV}$) exhibit a conventional left and right circularly polarized Zeeman photoluminescence doublet in applied magnetic fields. In contrast, nanocrystals with large ${\Delta }_{XY}$ ($>1\mathrm{meV}$) show an anomalous magnetophotoluminescence 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.