Spin Lifetime Tuning in Zincblende Heterostructures and Tions to Spin Devices
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SPIN LIFETIME TUNING IN ZINCBLENDE HETEROSTRUCTURES AND APPLICATIONS TO SPIN DEVICES ` ∗ , D. Z.-Y. TING† , Y.-C. CHANG X. CARTOIXA Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA † Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA ABSTRACT We present analytical expressions for the D’yakonov-Perel’ spin relaxation rates under the combined action of bulk and structural inversion asymmetry for [111] zincblende heterostructures when terms up to linear and third order in k are included in the Hamiltonian. We see for [111] heterostructures that, under the right conditions, the lowest-order-in-k component of the spin relaxation tensor can be made to vanish for all spin components at the same time. We study how the inclusion of terms of higher order in k affects these results. We finally discuss a proposal for a resonant spin lifetime transistor (RSLT) using the spin lifetime tuning concepts presented above, where the characteristics of the [111] device give the designer an added degree of freedom on the direction of the injected spins. 1. INTRODUCTION If the current pace of electronic device miniaturization is to continue, it is reasonable to think that the good use of the quantum properties of the electron will play a role in making this possible. Traditionally it has been the wave character of the electron that has been put to this use, resulting in devices such as the resonant tunnel diode [1] and the single electron transistor [2]. Another quantum property of the electron that only recently has received attention for its potential for information storage and processing is its spin. One of the key parameters that must be controlled for the successful achievement of spin electronic (spintronic) devices, such as the Datta-Das transistor [3], is the spin lifetime of the carriers. For the transport of spin-encoded quantum (single state) or classical (average over an ensemble) information, we naturally demand spin lifetimes as long as possible. If, as it is normally the case, we are to employ heterostructures in the design of our spintronic devices, we need tools that provide us with predictions about the spin lifetimes and direct us to ways of obtaining the goal of long spin lifetimes. The lack of an inversion symmetry center lifts the double degeneracy at a general k point in the Brillouin zone, thus greatly reducing the spin lifetime of electrons. In this paper we investigate how the interplay of structural inversion asymmetry [4] (SIA) and bulk inversion asymmetry [5] (BIA) affects the D’yakonov-Perel’-Kachorovski˘ı [6, 7] spin lifetimes for electrons in [111] quantum wells (QWs). The effects of SIA on the spin dynamics should always be kept in mind, as it can be unintentionally present in any heterostructure due to uneven doping profiles [8], surface effects, different interdiffusion at the boundaries, etc. We start, in Sec. 2, by computing the effective spin Hamiltonian in a two-band model. In Sec. 3 we then proceed to compute the en
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