Effect of pump-probe detuning on the Faraday rotation and ellipticity signals of mode-locked spins in InGaAs quantum dots

TL;DR

This study investigates how pump-probe detuning affects Faraday rotation and ellipticity signals in quantum dot ensembles, revealing distinct behaviors for degenerate and detuned conditions and providing insights into electron spin dynamics.

Contribution

It presents experimental observations and theoretical analysis of spin signals in quantum dots under varying pump-probe detuning, advancing understanding of spin precession and g-factor dependence.

Findings

Faraday rotation signal amplitude initially increases then decays with pump-probe separation for degenerate conditions.

Ellipticity signal consistently decays with separation, regardless of detuning.

Experimental data aligns with a microscopic theory, elucidating spectral dependence of electron spin precession.

Abstract

We have studied the Faraday rotation and ellipticity signals in ensembles of singly-charged (In,Ga)As/GaAs quantum dots by pump-probe spectroscopy. For degenerate pump and probe we observe that the Faraday rotation signal amplitude first grows with increasing the time separation between pump and probe before a decay is observed for large temporal separations. The temporal behavior of the ellipticity signal, on the other hand, is regular: its amplitude decays with the separation. By contrast, for detuned pump and probe the Faraday rotation and ellipticty signals both exhibit similar and conventional behavior. The experimental results are well described in the frame of a recently developed microscopic theory [Phys. Rev. B 80, 104436 (2009)]. The comparison between calculations and experimental data allows us to provide insight into the spectral dependence of the electron spin precession frequencies and extract the electron g-factor dependence on energy.