Full Electrical Control of the Electron Spin Relaxation in GaAs Quantum Wells

Abstract

The electron spin dynamics in (111)-oriented GaAs/AlGaAs quantum wells is studied by timeresolved photoluminescence spectroscopy. By applying an external field of 50 kV/cm a two-order of magnitude increase of the spin relaxation time can be observed reaching values larger than 30 ns; this is a consequence of the electric field tuning of the spin-orbit conduction band splitting which can almost vanish when the Rashba term compensates exactly the Dresselhaus one. The measurements under transverse magnetic field demonstrate that the electron spin relaxation time for the three space directions can be tuned simultaneously with the applied electric field.The control of the electron spins in semiconductors for potential use in transport devices or quantum information applications has attracted a great attention in recent years [1][2][3]. In 2D nanostructures made of III-V or II-VI semiconductors, the dominant loss of electron spin memory is related to the spin relaxation mechanism known under the name Dyakonov-Perel (DP) [4,5]. In these materials, the absence of inversion symmetry and the spin-orbit (SO) coupling are responsible for the lifting of degeneracy for spin | 1/2 and | −1/2 electrons states in the conduction band (CB). This splitting plays a crucial role for the spin manipulation and spin transport phenomena [6,7]. As it depends strongly on the crystal and nanostructure symmetry [8][9][10], it can be efficiently tailored as explained below. The SO splitting can be viewed as the result of the action on the electron spin of an effective magnetic field whose amplitude and direction depend on the wave vector k of the electron. The electronic spin will precess around this field with an effective, momentum dependent, Larmor vector Ω whose magnitude corresponds to the CB spin splitting. This effective magnetic field changes with time since the direction of electron momentum varies due to electron collisions. As a consequence, spin precession around this field in the intervals between collisions gives rise to spin relaxation. In the usual case of frequent collisions, the relaxation time of an electron spin oriented along the direction i can be written [4]:where Ω 2 ⊥ is the mean square precession vector in the plane perpendicular to the direction i (i=x, y, z) and τ * p the electron momentum relaxation time. This yields the loss of the electron spin memory in a few tens or hundreds of picoseconds [11,12]. As the driving force in the DP spin relaxation is the SO splitting, its reduction is expected to lead to an increase of the spin relaxation time [13,14]. In bulk zinc blende semiconductor, the Bulk Inversion Asymmetry (BIA) spin splitting, also called Dresselhaus term, is determined by [1,8]:where γ is the Dresselhaus coefficient and k = (k x , k y , k z ) the electron wavector. In a quantum well (QW) where the momentum component along the growth axis z is quantized, the vector Ω due to the BIA for the lowest electron sub-band writes:where k 2 z is the averaged squared wavevector along the growth direction and k the...

Long-lived spin coherence of indirect excitons in GaAs coupled quantum wells

“…This may be achieved through localisation of indirect excitons. In such a case, electric-field-induced modifications of spin-orbit interactions [4,19] would not be dominant. This conclusion is further supported by the weak variation (within our instrumental precision of ∼ 100 μeV) of the energy splitting between | + 1 and | − 1 energy levels ( fig.…”

Strongly anisotropic spin relaxation revealed by resonant spin amplification in (110) GaAs quantum wells

“…Taking into account a broad spread in experimentally reported values of γ from 5 to 28 eVÅ 3 (Refs. [35][36][37][38][39][40][41], one can estimate that the required asymmetry n lies in the range between ∼0.5 × 10 11 and ∼3 × 10 11 cm −2 . Second, the random electric field of the dopants, assuming that they are not fully screened by the charge carriers in the AlAs layers, 32 leads to a random Rashba 085313-3 field and spin relaxation rate,…”

Effect of the Pauli principle on photoelectron spin transport inp+GaAs

“…Experimental investigations including the use of novel techniques such as spin gratings [8] or spin noise [9] reveal that these phenomena arise from one of two possible coupling mechanisms, either spin-charge or spin-spin couplings. In the former, the spin-orbit interaction plays a central role and gives rise to the extrinsic spin Hall effect and the spin helix, as well as providing the basis for the electrical manipulation of spin [10][11][12]. Spin-spin coupling, on the other hand, results in spin Coulomb drag [3] and a spin-dependent density of states via bandgap renormalization [13].…”