Spin-Transistor Action via Tunable Landau-Zener Transitions

Abstract

Spin-transistor designs relying on spin-orbit interaction suffer from low signal levels resulting from low spin-injection efficiency and fast spin decay. Here, we present an alternative approach in which spin information is protected by propagating this information adiabatically. We demonstrate the validity of our approach in a cadmium manganese telluride diluted magnetic semiconductor quantum well structure in which efficient spin transport is observed over device distances of 50 micrometers. The device is turned "off" by introducing diabatic Landau-Zener transitions that lead to a backscattering of spins, which are controlled by a combination of a helical and a homogeneous magnetic field. In contrast to other spin-transistor designs, we find that our concept is tolerant against disorder.

Spin transmission control in helical magnetic fields

“…We further show that transitions between transport modes induced by orbital coupling, which was not considered in Ref. 6, may enhance the resistance modulation in partially polarized waveguides.…”

“…The mean free paths l e and the ratios l e /a in the calculations are of the order of those which are attained in (Cd,Mn)Te quantum wells. 6 In partially spin-polarized systems Zeeman-split eigenstates φ ± of spin-compensated modes both remain below the Fermi energy [see dashed lines in Fig. 6(a)].…”

“…6 This leads effectively to a tunable backscattering of spins which changes conductance and the degree of spin polarization of transmitted electrons in the device. The validity of this approach was shown in transport experiments 6 in magnetically modulated diluted (Cd,Mn)Te magnetic semiconductor quantum wells where the s-d exchange interaction between electronic states and the localized magnetic moments of the Mn atoms gives rise to an enhanced g factor and a giant Zeeman splitting. 7 In the low-field limit at low temperatures the g factor is approximately constant with values ranging up to several hundreds.…”

“…The giant Zeeman coupling is more than an order of magnitude larger than the Rashba and the Dresselhaus spin-orbit couplings in these magnetic fields. 6 Motivated by these experiments, here we consider spin transmission control in helical magnetic fields in the presence of spin-independent disorder scattering and magnetic field coupling to orbital dynamics. We calculate spin transport in a two-terminal model device, sketched in Fig.…”

Observation of the spin Nernst effect

“…While first experiments in the spirit of the spin Hall effect have been conducted in the 1970s [18] , only recently, electrically driven transverse spin transport in the form of the spin Hall effect (SHE) [19,20] resulted in a new paradigm for spin-electronic device design [3,21,4]. The SHE refers to a transverse pure spin current j SH s ∝ θ SH j c × s driven by a charge current density j c , see Fig.…”