Takaaki Koga

Competition between spin-orbit interaction and Zeeman coupling in Rashba two-dimensional electron gases

We systematically investigate how the interplay between the Rashba spin-orbit interaction and Zeeman coupling affects the electron transport and the spin dynamics in InGaAs-based 2D electron gases. From the quantitative analysis of the magnetoconductance, measured in the presence of an in-plane magnetic field, we conclude that this interplay results in a spin-induced breaking of time reversal symmetry and in an enhancement of the spin relaxation time. Both effects are due to a partial alignment of the electron spin along the applied magnetic field, and are found to be in excellent agreement with recent theoretical predictions. Achieving control of the orbital motion of electrons by acting on their spin is a key concept in modern spintronics and is at the basis of many proposals in the field of quantum information. 1 Two physical mechanisms are used to influence the dynamics of the electron spin in normal conductors: spinorbit interaction (SOI) and Zeeman coupling. In the presence of elastic scattering, these two mechanisms affect the spin in different ways. SOI is responsible for the randomization of the spin direction whereas the Zeeman coupling tends to align the spin along the applied magnetic field. Depending on the relative strength of these interactions, this interplay of SOI and Zeeman coupling is responsible for the occurrence of a variety of physical phenomena. 2,3 Quantum wells (QW’s ) that define two-dimensional electron gases (2DEG’s ) are particularly suitable for the experimental investigation of the competition between SOI and Zeeman coupling, since they give control over many of the relevant physical parameters. Specifically, in these systems the SOI strength can be controlled by an appropriate QW design 4 and by applying a voltage to a gate electrode. 5,6 The electron mobility is usually density dependent, so that the elastic scattering time can also be tuned by acting on the gate. Finally, Zeeman coupling to the spin can be achieved with minimal coupling to the orbital motion of the electrons by applying a magnetic field parallel to the conduction plane. In this Communication we study the competition of SOI and Zeeman coupling via magnetoconductance measurements in InGaAs-based 2DEG’s with different Rashba SOI strength. From the detailed quantitative analysis of the weak antilocalization as a function of an applied in-plane magnetic fieldsBid, we find that the partial alignment of the spin along Bi results in a spin-induced time reversal symmetry (TRS) breaking, and in an increase of the spin relaxation time. The increase in spin relaxation time is found to be quadratic with Bi, and strongly dependent on the SOI strength and the elastic scattering time. For both the spin-induced TRS breaking and the increase in spin relaxation time we find excellent quantitative agreement with recent theory. We also show that the quantitative analysis permits us to determine the in-plane g factor of the electrons. The three InAlAs/ InGaAs/ InAlAs quantum wells used in our work are very similar to those described in detail elsewhere. 4 Here, we recall that each well is designed to have a different (Rashba) SOI strength. The characteristic spin-split energy D for the different samples is D < 0.5 1.5, and 1.8 meV (in what follows we will refer to these samples as to samples 1, 2, and 3, respectively). The electron density and mobility at Vgate = 0 V are n. 7 3 10 15 m ˛2 and m . 4 m 2 / V s. All measurements have been performed on s203 80 mmd Hall-bar shaped devices, at 1.6 K. A 14 T superconducting magnet is used to generate Bi and homemade split coils mounted on the sample holder are used to independently control the perpendicular fieldsB’d. No significant difference in the results is observed when the in-plane field is applied parallel or perpendicular to the direction of current flow.

Effect of an InP / In0.53Ga0.47As interface on spin-orbit interaction in In0.52Al0.48As/ In0.53Ga0.47As heterostructures

We report the effect of the insertion of an InP/In

Gate-controlled electron g factor in an InAs-inserted-channel In0.53Ga0.47As/In0.52Al0.48As heterostructure

_{0.53}

Spin-orbit induced interference of ballistic electrons in polygon structures

Ga

Statistical significance of the fine structure in the frequency spectrum of Aharonov-Bohm conductance oscillations

_{47}

Nonmagnetic control of spin transport in InGaAs quantum wells

As Interface on Rashba spin-orbit interaction in In

Effect of spin–orbit interaction in an InGaAs-based Aharonov–Bohm ring structure

_{0.52}

Structural Control of Rashba Spin–Orbit Coupling in In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As Quantum Wells

Al

Ballistic spin interferometer using the Rashba effect

_{0.48}

Electron g factor in a gated InGaAs channel with double InAs-inserted wells

As/In