L-valley electron spin dynamics in GaAs

Abstract

Optical orientation experiments have been performed in GaAs epilayers with photoexcitation energies in the 3 eV region yielding the photogeneration of spin-polarized electrons in the satellite L valley. We demonstrate that a significant fraction of the electron spin memory can be conserved when the electron is scattered from the L to the Γ valley following an energy relaxation of several hundreds of meV. Combining these high energy photo-excitation experiments with time-resolved photoluminescence spectroscopy of Γ valley spin-polarized photogenerated electrons allows us to deduce a typical L valley electron spin relaxation time of 200 fs, in agreement with theoretical calculations.PACS numbers: 72.25. Rb, 72.25.Fe, 78.55.Cr The electron spin dynamics have been studied in great detail for about 50 years in semiconductors thanks to the optical orientation technique [1, 2]. However all these experiments were performed with optical excitation energies close to the band gap (typically 1.5 -2 eV in GaAs), yielding the photogeneration of spin-polarized electrons in the Γ valley. In addition to its fundamental aspect, the knowledge of the electron spin dynamics of electrons in the upper valleys is of great interest for spintronic devices such as Spin-LEDs or Spin-Lasers, where the electrical spin injection can lead to electrons populating not only the Γ valley but also the satellite L and X valleys whose spin dynamics is almost unknown. In Spin-LEDs based on a Ferromagnetic (FM) layer and Schottky barrier, it was predicted with Monte Carlo simulations that strong electric fields at the interfaces between the FM and the semiconductor layer lead to the redistribution of electrons among several valleys (L and X), where the spin relaxation times have been predicted to be much shorter than the one in the Γ valley [3][4][5][6]. These upper valley electrons thus play a crucial role in the operation of Spin-LED and Spin laser devices [6]. For the demonstration of the Spin Gunn effect predicted a few years ago it is also essential to get information about the spin relaxation times of high energy electrons in the L valley [7]. Very little is known about the spin polarization and the spin dynamics of the high energy electrons in these L valleys in GaAs, though intervalley scattering in zincblende semiconductors has for a long time been a subject of theoretical and experimental interest [8][9][10]. The Dresselhaus intrinsic spin splitting, which is a key parameter for the spin polarization properties has been mainly studied in the close vicinity near the Brillouin zone center k 0 = Γ [11]. The spin-orbit coupling parameters in the upper valleys, for k 0 =L or k 0 =X have been calculated recently by different groups [11][12][13]. Compared to the Γ valley of III-V semiconductors, larger k-dependent spin splittings in the surrounding of the L point were predicted [13].As a consequence the D'Yakonov-Perel spin relaxation mechanism in the L valleys is expected to be very efficient. Multivalley spin relaxation in the presence of high ...

Wide-range optical spin orientation in Ge from near-infrared to visible light

“…However, no experimental data for excitation far from the point of the Brillouin zone (BZ) have been reported so far. Even for GaAs, only very recently the photon energy dependence of optical spin orientation well above the absorption edge has been reported [14].In this Rapid Communication, we report on the spectral dependence of the optical spin orientation in Ge at room temperature and over a wide spectral range (400-1550 nm, corresponding to 3.1-0.8 eV), via measurements of the helicitydependent photocurrent on Ge-based spin PDs. Surprisingly enough, the maximum sensitivity to photon helicity is observed far away from the direct gap (0.8 eV), where optical pumping is supposed to produce the highest initial spin polarization.…”

“…However, no experimental data for excitation far from the point of the Brillouin zone (BZ) have been reported so far. Even for GaAs, only very recently the photon energy dependence of optical spin orientation well above the absorption edge has been reported [14].…”

Ab Initio Approaches for Low‐Energy Spin Hamiltonians

“…[133] It was argued that a finite Dzyaloshinskii-Moriya interaction plays the role of a vector potential in the electronic case. The effect of a finite DM interaction in a ferromagnetic pyrochlore structure is thought to induce a topological magnon insulator state with chiral edge modes [134,135] and the appearance of magnon Weyl points. [136] From an experimental standpoint, the underlying spin Hamiltonian remains somewhat controversial.…”

Endommagement des alliages métalliques par les neutrons rapides

“…Bien qu'aucune bulle d'hélium n'ait pu être observée aux joints de grains dans les échantillons implantés à 250°C, l'hypothèse raisonnable est que l'hélium à l'état d'atomes ou d'amas nanométriques puisse abaisser l'énergie de cohésion des joints de grains [9]. Pour des joints de géométrie simple, cette hypothèse est en accord qualitatif avec des résultats récents de calculs ab initio d'énergie de cohésion dans le fer [10].…”