Spin noise spectroscopy: hole spin dynamics in semiconductor quantum dots

Abstract

Spin noise spectroscopy can be an extraordinary efficient, all-optical and low-perturbing tool to study the equilibrium spin dynamics in semiconductors. However, great care is necessary for studying the spin dynamics in inhomogeneous quantum dot ensembles. First, we show measurements on the spin dynamics of localized holes in (InGa)As quantum dots ensembles. The experiments reveal a very slow longitudinal spin relaxation time T l and a moderately slow transverse spin relaxation time T 2 * which results from the finite hyperfine interaction of the hole spins due to heavy-light hole mixing in (InGa)As quantum dots. The longitudinal spin relaxation rate shows a linear dependence on the probe intensity which suggests a linear extrapolation to zero intensity for the extraction of the intrinsic spin relaxation rate. However, calculations reveal that the intrinsic heavy-hole spin relaxation is easily shadowed in quantum dot ensembles by effects of finite absorption even if the majority of quantum dots is well out of resonance of the probe laser. For typical laser intensities and very long spin relaxation times, a linear extrapolation to zero intensity is therefore not allowed. What is more, the line shape of the spin noise spectra changes from Lorentzian to non-Lorentzian with increasing laser intensity which can be easily misinterpreted as an intrinsic non-exponential spin relaxation process.