Femtosecond study of the interplay between excitons, trions, and carriers in (Cd,Mn)Te quantum wells

TL;DR

This study investigates ultrafast spin dynamics and interactions among excitons, trions, and carriers in (Cd,Mn)Te quantum wells using femtosecond spectroscopy, revealing new insights into charge screening and oscillator strength phenomena.

Contribution

It introduces a novel explanation for oscillator strength stealing based on charge carrier screening and examines the impact of trion formation on hole spin polarization.

Findings

Hole polarization is induced by trion formation.

Charge carrier screening affects exciton oscillator strength.

Trion formation influences spin dynamics and screening effects.

Abstract

We present an absorption study of the neutral and positively charged exciton (trion) under the influence of a femtosecond, circularly polarized, resonant pump pulse. Three populations are involved: free holes, excitons, and trions, all exhibiting transient spin polarization. In particular, a polarization of the hole gas is created by the formation of trions. The evolution of these populations is studied, including the spin flip and trion formation processes. The contributions of several mechanisms to intensity changes are evaluated, including phase space filling and spin-dependent screening. We propose a new explanation of the oscillator strength stealing phenomena observed in p-doped quantum wells, based on the screening of neutral excitons by charge carriers. We have also found that binding heavy holes into charged excitons excludes them from the interaction with the rest of the system, so that oscillator strength stealing is partially blocked