Bright-Exciton Fine Structure and Anisotropic Exchange in CdSe Nanocrystal Quantum Dots

TL;DR

This study uses high magnetic fields and polarization-resolved spectroscopy to reveal a significant intrinsic fine structure splitting in bright excitons of CdSe nanocrystals, advancing understanding of their spin properties.

Contribution

It provides the first detailed measurement of the bright exciton fine structure splitting caused by anisotropic exchange in colloidal CdSe nanocrystals.

Findings

Large (1-2 meV) intrinsic fine structure splitting detected

Polarization-resolved PL reveals spin-flipped bright excitons at high fields

Supports understanding of exciton spin dynamics in nanocrystals

Abstract

We report on polarization-resolved resonant photoluminescence (PL) spectroscopy of bright (spin-1) and dark (spin-2) excitons in colloidal CdSe nanocrystal quantum dots. Using high magnetic fields to 33 T, we resonantly excite (and selectively analyze PL from) spin-up or spin-down excitons. At low temperatures (<4K) and above ~10 T, the spectra develop a narrow, circularly polarized peak due to spin-flipped bright excitons. Its evolution with magnetic field directly reveals a large (1-2 meV), intrinsic fine structure splitting of bright excitons, due to anisotropic exchange. These findings are supported by time-resolved PL studies and polarization-resolved PL from single nanocrystals.