"Spin"-flip scattering of holes in semiconductor quantum wells

Distinguishing the inverse spin Hall effect photocurrent of electrons and holes by comparing to the classical Hall effect

The photo-excited electrons and holes move in the same direction in the diffusion and in the opposite direction in the drift under an electric field. Therefore, the contribution to the inverse spin Hall current of photo-excited electrons and holes in the diffusion regime is different to that in the drift regime under electric field. By comparing the classical Hall effect with the inverse spin Hall effect in both diffusion and drift regime, we develop an optical method to distinguish the contributions of electrons and holes in the inverse spin Hall effect. It is found that the contribution of the inverse spin Hall effect of electrons and holes in an InGaAs/AlGaAs un-doped multiple quantum well is approximately equal at room temperature.

Optical injection and terahertz detection of the macroscopic Berry curvature

We propose an experimental scheme to probe the Berry curvature of solids. Our method is sensitive to arbitrary regions of the Brillouin zone and employs only basic optical and terahertz techniques to yield a background-free signal. Using semiconductor quantum wells as a prototypical system, we discuss how to inject Berry curvature macroscopically and probe it in a way that provides information about the underlying microscopic Berry curvature.

Spin coherence of holes in GaAs/(Al,Ga)As quantum wells

Carrier spin coherence in a p-doped GaAs/(Al,Ga)As quantum well with a diluted hole gas is studied by picosecond pump-probe Kerr rotation. For resonant optical excitation of the positively charged exciton the spin precession shows two types of oscillations: Electron spin beats decaying with the charged exciton radiative lifetime of 50 ps, and long-lived hole spin beats with dephasing times up to 650 ps, which decrease with increasing temperature, underlining the importance of hole localization. The mechanism of hole spin coherence generation is discussed.

ASYMMETRIC DOUBLE QUANTUM WELLS AS EXCITON SPIN SEPARATOR

Exciton recombination in asymmetric CdMgTe / CdTe / CdMgTe / CdTe / CdMnTe double quantum wells (ADQW) with different barrier widths is studied in magnetic field up to 10 T. As grown structures were subjected to temperature annealing to introduce Mn and Mg atoms from the barriers into the CdTe quantum wells (QW). At low fields exciton transition in QW with magnetic impurity ( Mn ) is higher in energy than that in QW with nonmagnetic impurity ( Mg ), and interwell exciton relaxation is fast independently on the spin state. In contrast, at high fields, when the energy order reverses, an unexpectedly low relaxation rate of σ- polarized excitons from nonmagnetic QW to the ground σ+ polarized state in magnetic QW has been observed. Effect strongly correlates with hh–lh splitting value Δhh – lh and discussed in terms of valence band mixing. Such a slowing down of relaxation allows separation of oppositely polarized excitons in different QWs.

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

We study the absorption by neutral excitons and positively charged excitons (trions) following 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 gas of free holes is created by the formation of trions. The evolution of these populations is described, including spin flip and trion formation. We evaluate the contributions of phase space filling and spin-dependent screening. We propose a new explanation of the oscillator strength stealing phenomena observed in doped quantum wells, based on the screening of neutral excitons by charge carriers. We have also found that binding holes into charged excitons excludes them from the interaction with the rest of the system, so that oscillator strength stealing is partially blocked.

Spin-sensitive bleaching and monopolar spin orientation in quantum wells

Spin-sensitive bleaching of the absorption of far-infrared radiation has been observed in p-type GaAs/AlGaAs quantum well structures. The absorption of circularly polarized radiation saturates at lower intensities than that of linearly polarized light due to monopolar spin orientation in the first heavy-hole subband. Spin relaxation times of holes in p-type material in the range of tens of ps were derived from the intensity dependence of the absorption.