Electron spin relaxation in paramagnetic Ga(Mn)As quantum wells

Abstract

Electron spin relaxation in paramagnetic Ga(Mn)As quantum wells is studied via the fully microscopic kinetic spin Bloch equation approach where all the scatterings, such as the electron-impurity, electron-phonon, electron-electron Coulomb, electron-hole Coulomb, electron-hole exchange (the Bir-Aronov-Pikus mechanism) and the s-d exchange scatterings, are explicitly included. The ElliotYafet mechanism is also incorporated. From this approach, we study the spin relaxation in both n-type and p-type Ga(Mn)As quantum wells. For n-type Ga(Mn)As quantum wells where most Mn ions take the interstitial positions, we find that the spin relaxation is always dominated by the DP mechanism in the metallic region. Interestingly, the Mn concentration dependence of the spin relaxation time is nonmonotonic and exhibits a peak. This is due to the fact that the momentum scattering and the inhomogeneous broadening have different density dependences in the non-degenerate and degenerate regimes. For p-type Ga(Mn)As quantum wells, we find that the Mn concentration dependence of the spin relaxation time is also nonmonotonic and shows a peak. Differently, the cause of this behaviour is that the s-d exchange scattering (or the Bir-Aronov-Pikus) mechanism dominates the spin relaxation in the high Mn concentration regime at low (or high) temperature, whereas the DP mechanism determines the spin relaxation in the low Mn concentration regime. The Elliot-Yafet mechanism also contributes to the spin relaxation at intermediate temperatures. The spin relaxation time due to the DP mechanism increases with increasing Mn concentration due to motional narrowing, whereas those due to the spin-flip mechanisms decrease with it, which thus leads to the formation of the peak. The temperature, photo-excitation density and magnetic field dependences of the spin relaxation time in p-type Ga(Mn)As quantum wells are investigated systematically with the underlying physics revealed. Our results are consistent with the recent experimental findings.

Quantum kinetic equations for the ultrafast spin dynamics of excitons in diluted magnetic semiconductor quantum wells after optical excitation

“…Additionally, phonons do not couple directly to the spin and thus represent a secondary relaxation process which only becomes relevant in combination with other effects, such as spin-orbit coupling. Theoretical rate-equation models that include the scattering due to phonons also support that the s-d exchange interaction is the most important scattering mechanism at low temperatures 34 . Given that the recently reported 19 spin-lattice relaxation time of Mn 2+ ions in typical DMS quantum wells is on the order of µs, the coupling of phonons to the Mn system can also be disregarded on the typical ps time scale of the carrier spin relaxation 31,44,58 .…”

“…Note that the nonmagnetic scattering as well as the pd interaction do not influence the spin dynamics on the Markovian level, as follows from Eqs. (34).…”

“…But in many experiments, also the spin dynamics studied via optical pump-probe experiments is of interest 17,18,31 . Theoretical descriptions of such experiments are less developed in the literature and are typically based on rateequation models [12][13][14]17,[31][32][33][34][35] , coinciding with Fermi's golden rule for vanishing magnetic field. However, a number of experiments have provided strong evidence that these models fail to reproduce some of the pertinent characteristics of the spin dynamics in DMS.…”

Influence of nonmagnetic impurity scattering on spin dynamics in diluted magnetic semiconductors

“…For this purpose, spintronic devices based on semiconductors are preferable to metallic structures since the dephasing time in a metal is about three orders of magnitude shorter than in a semiconductor 4 . In the context of semiconductor spintronics [5][6][7] , a particularly interesting class of materials for future applications are diluted magnetic semiconductors (DMS) [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] , which are obtained when semiconductors are doped with transition metal elements, such as Mn, which act as localized magnetic moments. While some types of DMS, such as Ga 1−x Mn x As, exhibit a ferromagnetic phase 8,23 , other types of DMS, like the usually paramagnetic CdMnTe, are especially valued for the enhancement of the effective carrier g-factor by the giant Zeeman effect that can be used, e.g., to facilitate an injection of a spin-polarized current into a light-emitting diode 24 .…”

Effect of interfacial scattering on spin-dependent thermoelectric properties in diluted magnetic semiconductor layered structures

“…Hence, the selected effective mass of all carriers is consistent with the experimental parameters used in the present work. Also, the relaxation time is selected as s ¼ 10 À12 for both hole spins of GaMnAs [46]. Our numerical results are carried out at the temperature T ¼ 3 K.…”