Nonballistic Spin-Field-Effect Transistor

Abstract

We propose a spin field-effect transistor based on spin-orbit (s-o) coupling of both the Rashba and the Dresselhaus types. Differently from earlier proposals, spin transport through our device is tolerant against spin-independent scattering processes. Hence the requirement of strictly ballistic transport can be relaxed. This follows from a unique interplay between the Dresselhaus and the (gate-controlled) Rashba interactions; these can be tuned to have equal strengths thus yielding kindependent eigenspinors even in two dimensions. We discuss implementations with two-dimensional devices and quantum wires. In the latter, our setup presents strictly parabolic dispersions which avoids complications arising from anticrossings of different bands.In the recent years research in semiconductor physics has been focused on the emerging field of spintronics. This key word refers to the variety of efforts to use the electron spin rather than, or in combination with, its charge for information processing; or, even more ambitiously, quantum information processing [2]. Among the most prominent device proposals is the spin field-effect transistor (FET) due to Datta and Das [3]. This proposal uses the Rashba spin-orbit coupling to perform controlled rotations of spins of electrons passing through an FETtyped device. This particular spin-orbit interaction is due to the inversion-asymmetry of the confining potential and is of the form [4]where p is the momentum of the electron confined in a two-dimensional geometry, and σ the vector of Pauli matrices. The coefficient α is tunable in strength by the external gate of the FET. Due to the dependence on the momentum, the Rashba spin-orbit coupling can be viewed as a wave vector-dependent Zeeman field which can change drastically if the electron is scattered into a different momentum state. Therefore, such scattering events readily randomize the electron spin thus limiting the range of operation of the Datta-Das spin-FET to the regime of ballistic transport where such processes do not occur.In the present work we propose a modified version of the spin-FET in which the electrons are not only subject to spin-orbit interaction of the Rashba but also of the Dresselhaus type [5]. The latter is present in semiconductors lacking bulk inversion symmetry. When restricted to a two-dimensional semiconductor nanostruture with appropriate growth geometry this coupling is of the form [6,7] where the coefficient β is determined by the semiconductor material and the geometry of the sample. Below we show that our proposed device is robust against spin-independent scattering and hence can also operate in a non-ballistic (or diffusive) regime. This unique feature follows from the possibility of tuning the Rashba (via proper gating) and the Dresselhaus terms so that they have equal strengths α = β. In this case, we show quite generally below that the electron spinor is k-independent in two dimensions -even in the presence of (spin-independent) scatterers. Tuned Rashba and Dresselhaus terms. Consider the Ham...

Persistent oscillatory currents in a 1D ring with Rashba and Dresselhaus spin–orbit interactions excited by a terahertz pulse

“…As shown in Fig. 8(d) the critical values are 0, 2π/3, π, and 4π/3 (j = 0, 4,6,8). The time average of the spin current, I z t = (I z (T /2) + I z (T ))/2, is also plotted in Fig.…”

“…This phenomenology is embodied by the single particle Hamiltonian, H SO = α (σ x p y − σ y p x ) + β (σ x p x − σ y p y ) , (1) which introduces the Rashba and Dresselhaus interaction constants α and β which couple the electron momentum p = (p x , p y ) with the electron spin represented by the Pauli spin matrices, σ x,y . The superposition of the Rashba and Dresselhaus terms generates particularly interesting situations when their strengths are equal, such as the cancellation of dephasing for the eigenstate spinors and the ensuing ballistic spin transport 4 or the formation of a persistent spin helix. 5 In this paper, we investigate the consequences of the Rashba-Dresselhaus superposition on spin and charge currents that are being induced in a quasi-onedimensional ring by a terahertz laser pulse with a spatial asymmetry.…”

Electrical spin injection from ferromagnet into an InAs quantum well through a MgO tunnel barrier

“…On the other hand, for gate control of the channel spin state is another issue to achieve spin transistor. For this purpose, InAs is known to be a good candidate material for spin channel in a Datta-Das spin transistor for its high spin orbit interaction [12][13][14][15] . The band offset and carrier distribution was found to affect the Rashba SOI strength strongly and gate electric field in InAlAs/InGaAs metamorphic heterostructures make it possible to control it.…”

Spin Relaxation: From 2D to 1D

“…On the other hand, the range of operation of the spin transistor is limited by the spin relaxation mechanism induced by the spin-orbit interaction [15][16][17]. Here, we describe the possibility of an effective suppression of the spin relaxation in the two-dimensional conducting channel of a spin transistor [18][19][20][21].…”

“…In addition to the gate voltage, the transconductance can be also controlled via an external magnetic field. Rather than a new electronic device, the spin transistor initiated many studies on spin-polarized transport and spin-injection phenomena in semiconductor/ferromagnetic junctions [8][9][10][11][12][14][15][16][17]. The spin transistor relies upon controlling the precession of the electron spin in the conducting channel due to the influence of the Rashba term.…”