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Exciton Spin Relaxation (exciton + spin_relaxation)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Magneto-optical spectroscopy of spin injection and spin relaxation in ZnMnSe/ZnCdSe and GaMnN/InGaN spin light-emitting structures

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2007
I. A. Buyanova
Abstract In this paper we review our recent results from in-depth investigations of physical mechanisms which govern efficiency of several processes important for future spintronic devises, such as spin alignment within diluted magnetic semiconductors (DMS), spin injection from DMS to non-magnetic spin detectors (SDs) and also spin depolarization within SD. Spin-injection structures based on II,VIs (e.g. ZnMnSe/Zn(Cd)Se) and III,Vs (e.g. GaMnN/Ga(In)N) were studied as model cases. Exciton spin relaxation within ZnMnSe DMS, important for spin alignment, was found to critically depend on Zeeman splitting of the exciton states and is largely facilitated by involvement of longitudinal optical (LO) phonons. Optical spin injection in ZnMnSe/Zn(Cd)Se was shown to be governed by (i) commonly believed tunneling of individual carriers or excitons and (ii) energy transfer via localized excitons and spatially separated localized electron,hole pairs (LEHP) located within DMS. Unexpectedly, the latter mechanism is in fact found to dominate spin injections. We shall also show that spin depolarization in the studied structures is essentially determined by ef- ficient spin relaxation within non-magnetic spin detectors, which is an important factor limiting efficiency of spin detection. Detailed physical mechanisms leading to efficient spin depolarization will be discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Exciton states and tunneling in semimagnetic asymmetric double quantum wells

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2010
S. V. Zaitsev
Abstract Exciton level structure and interwell relaxation are studied in Cd(Mn,Mg)Te-based asymmetric double quantum wells (ADQWs) by a steady-state optical spectroscopy in magnetic fields up to B,=,10,T. The as grown heterostructures with CdTe QWs and nonmagnetic interwell CdMgTe barrier were subjected to a rapid temperature annealing to introduce Mn and Mg atoms from opposite barriers inside the QWs which results in a formation of the ADQW with completely different magnetic field behavior of the intrawell excitons. The giant Zeeman effect in the QW with magnetic Mn ions gives rise to a crossing of the ground exciton levels in two QWs at BC,,,3,6,T which is accompanied by a reverse of the interwell tunneling direction. In a single-particle picture the exciton tunneling is forbidden at B,<,1,T as supported by calculations. Experimentally, nevertheless, a very efficient interwell relaxation of excitons is found at resonant excitation in the whole magnetic field range, regardless of the tunneling direction, emphasizing importance of excitonic correlations in the interwell tunneling. At nonresonant excitation an unexpectedly slow relaxation of the ,, -polarized excitons from the nonmagnetic QW to the ,+ -polarized ground state in the semimagnetic QW is observed at B,>,BC, giving rise to a nonequilibrium distribution of excitons in ADQW. A strong dependence of the total circular polarization degree on the hh,lh splitting ,hh,lh in the nonmagnetic QW is found and attributed to the spin dependent interwell tunneling controlled by an exciton spin relaxation. Different charge-transfer mechanisms are analyzed in details and an elastic scattering due to a strong disorder is suggested as the main tunneling mechanism with the underlying influence of the valence band-mixing. [source]

Exciton-spin relaxation in weakly confining quantum dots due to spin,orbit interaction

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2006
E. Tsitsishvili
Abstract In weakly confining quantum structures such as interfacial islands or quantum disks the exciton-spin relaxation is governed by two independent electron and hole spin flip processes between the optically active and dark states. A microscopic theory for these transitions is presented which is based on second order spin,orbit and carrier,phonon interaction processes. We found that the sequential relaxation between bright and dark states leads to much faster exciton-spin relaxation than for strongly confining ("small") quantum dots where the dominant process stems from electron,hole exchange interaction plus hole deformation potential coupling. In addition, the fast exciton spin relaxation implies that the (exciton-bound) electron spin flip time is also much shorter than for a single electron. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Mechanisms of exciton spin relaxation in quantum dots

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2003
E. Tsitsishvili
Abstract We study the phonon-assisted relaxation processes (longitudinal relaxation time T1) within the radiative doublet of the heavy-hole-exciton in asymmetrical quantum dots. Two different relaxation mechanisms are considered: the exciton spin,acoustic phonon coupling via the strain-dependent short-range exchange interaction and the second-order quasielastic interaction between charge carriers and LO phonons. For zero magnetic fields and low temperatures, the calculated relaxation times for typical QDs are very long compared to the exciton lifetime yet they are strongly reduced in high magnetic fields (of the order of a few Tesla) and high temperatures T , 100 K. [source]