Rashba spin-orbit coupling in InGaAs/InP quantum wires
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Rashba spin-orbit coupling in InGaAs/InP quantum wires
Jens Knobbe, Vitaliy A. Guzenko and Thomas Schäpers Institute of Thin Films and Interfaces (ISG-1), Research Centre Jülich, 52425 Jülich, Germany ABSTRACT The effect of Rashba spin-orbit coupling on the transport properties of InGaAs/InP quantum wire structures is investigated. The geometry of the wire structures was defined by selective wet chemical etching. For wires without a gate a clear beating pattern, due to the presence of the Rashba spin-orbit coupling, is observed for wires with a width down to 600 nm. For narrower wires no beating pattern is found. The experimental observations are explained by contribution of the Rashba spin-orbit coupling to the one-dimensional magnetosubbands. By depleting the onedimensional conductor by means of a gate electrode the Rashba coupling strength could be controlled.
INTRODUCTION Spin related phenomena in semiconductors have attracted a lot of attention in recent years, owing to their potential for future spin electronic circuits [1]. For a successful implementation of spin electronic devices two basic requirements have to be fulfilled. First, it must be possible to inject spins into the semiconductor structure, which are well aligned along a particular orientation. This can be achieve by means of metallic ferromagnetic electrodes or by dilute magnetic semiconductors [2]. The second requirement is an efficient control of the electron spin within the device. In this respect the Rashba effect [3] is an interesting option, since it allows to adjust the spin precession of electrons in a two-dimensional electron gas by applying a gate voltage. An often cited example of a spin electronic device based on the Rashba effect is the spin transistor proposed by Datta and Das [4]. Following this approach, many novel device concepts have been developed [5-7]. The Rashba effect originates from the spin-orbit coupling due to a macroscopic electric field in a two-dimensional electron gas (2DEG). The Rashba spin-orbit coupling leads to a spinsplitting of the electron subbands in the 2DEG according to: E z = E zsub +
h2k 2 ±αR k , 2m *
(1)
where Esub denotes the subband energy of the 2DEG, m* is the effective electron mass and k is the wave vector within the plane of the 2DEG. The strength of the Rashba spin-orbit coupling is quantified by the parameter αR. The Rashba effect is most pronounced in low band gap channel layers like InAs or InGaAs. According to Eq. (1) the spin-splitting leads to a characteristic beating pattern in the Shubnikov-de Haas oscillations of the 2DEG, due to the splitting into two subbands with different effective electron concentrations [8,9]. It was demonstrated that the spinorbit coupling can be adjusted by changing the symmetry of the quantum well containing the 2DEG by means of a gate electrode [10,11]. Many concepts of spin electronic devices rely on
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a)
InP
10 nm
Etch Stop Layer
In0.53Ga0.47As
70 nm
Cap Layer
In0.77Ga0.23As
10 nm
Channel
InP
20 nm
Barrier
10 nm
Doping Laye
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