Optical Stark metrology of CdSe quantum dots: Reconciling the size-dependent oscillator strength with theory

TL;DR

This study uses the optical Stark effect to measure the exciton oscillator strength in CdSe quantum dots, confirming size-dependent predictions of the effective mass approximation and resolving previous experimental discrepancies.

Contribution

It demonstrates that the oscillator strength in CdSe quantum dots aligns with theoretical EMA predictions using optical Stark measurements.

Findings

Oscillator strength follows size-dependent EMA predictions

Femtosecond Stark shifts exceed 100 T pseudo-magnetic fields

Resolves previous experimental inconsistencies

Abstract

The $k\cdot p$ effective mass approximation (EMA) predicts large, nearly size-independent exciton oscillator strengths in quantum confined semiconductors. Yet, experimental reports have concluded that the total oscillator strength of the lowest-energy (1S$_{3/2}$1S$_{\text{e}}$) excitons in strongly confined CdSe NQDs is small and strongly size-dependent. Using the optical Stark effect, we show that the oscillator strength of the 1S$_{3/2}$1S$_{\text{e}}$ excitonic absorption peak in CdSe NQDs follows the predictions of the EMA. These oscillator strengths enable helicity-selective unsaturated Stark shifts corresponding to femtosecond pseudo-magnetic fields exceeding 100 T.