Transient diffusive spin dynamics in intrinsic InGaAs/InAlAs multiple quantum wells

Abstract

Spatial and temporal diffusive spin dynamics in the transient regime for 10-nm-wide InGaAs/InAlAs quantum wells were investigated using time-resolved optical Kerr rotation (TRKR) microscopy. The transient regime of diffusive spin dynamics is a specific regime which appears after local excitation but before the formation of a spin mode. In this regime, the spin precession frequency induced by the spin–orbit (SO) magnetic field decreases with time since the diffusive velocity decreases as the distribution of spins expands. In this study, by decreasing the spot size of the excitation pulse, we examined the spin dynamics in the transient regime. We carefully analyzed the TRKR signals using time-dependent frequency equations established by Kohda et al. [Appl. Phys. Lett. 107, 172402 (2015)]. All the TRKR signals could be well reproduced by the time-dependent frequency equations. Our analysis reveals that the spin precession frequencies arising from the SO interaction gradually decrease with time, and they allowed the extraction of the Rashba and Dresselhaus SO parameters. We revealed that SO parameters can be extracted accurately via scanning measurements in the diffusive motion of local spin excitation even in the time periods before the appearance of the spin mode.

Control of Spin Relaxation Anisotropy by Spin-Orbit-Coupled Diffusive Spin Motion

“…In addition, when σ eff decreases from 11.6 to 6.8 µm, the slope dΩ meas /dy increases gradually, which agrees well with Eq. ( 2) and which is consistent with earlier reports of the literature [20,22,23,[25][26][27]. For the x-scan [Fig.…”

“…Because SO fields are well defined for stationary electrons, the spin relaxation anisotropy has been regarded as a material constant. However, for moving electrons with a finite net velocity induced by drift [20][21][22][23][24][25] and diffusion [24][25][26][27], the electron trajectory further modulates SO fields and directly affects the spin relaxation anisotropy through the momentum-dependent spin precession. Moreover, the spin relaxation anisotropy is not limited to particular materials such as III-V semiconductors because the anisotropic SO fields are ubiquitous in solid states, with spin-momentum locking in topological insulators [28,29], Rashba interface in oxides [30], metal interfaces [31], and Zeeman-type SO field in 2D materials [32].…”

D’yakonov–Perel and Elliot–Yafet spin relaxation rates in InGaAs/InAlAs multiple quantum wells at room temperature

“…[21][22][23][24][25][26][27] Using this microscopic technique, clear in-plane and out-of-plane SO magnetic fields induced by the SOI were also observed with narrow-gap InGaAs/InAlAs QWs on the (001) and ( 110) substrates. [28][29][30][31] These results show that the DP and EY mechanisms competed in the InGaAs/InAlAs QWs. However, the EY mechanism is a spin relaxation mechanism that disturbs the spin manipulation and spin lifetime extension since EY mechanism is not originated from SO magnetic field.…”

“…In the microscopic setup, which observes the temporally and spatially resolved spin dynamics, the 350 μW quasicollinear pump and 100 μW probe pulses were focused on the sample via a 20× single objective lens; a spot size of s » 2 μm was achieved. [29][30][31] The focusing position of the probe pulse on the pump pulse was achieved by changing the angle of incidence of the pump pulse on the objective lens. For the macroscopic measurement, which observes the ensemble average of the spins, the 2 mW pump and 100 μW probe pulses were focused on the sample via a single lens with a focal length of 200 mm and a large spot size s > 100 μm was obtained.…”

Influence of Device Geometry and Imperfections on the Interpretation of Transverse Magnetic Focusing Experiments

“…For the Rashba coupling parameter, we used the value for an InGaAs-based 2DEG, eV m [ 3 ]. We note that other spin–orbit interactions such as the Dresselhaus effect are present in InGaAs [ 29 ], however they are not as strong as the Rashba effect, therefore we only included the Rashba effect in this paper for simplicity. The external magnetic field and Rashba spin–orbit coupling were applied everywhere in the system, including within the leads.…”