Resonant Tunneling Magneto Resistance in Coupled Quantum Wells

A three barrier resonant tunneling structure in which the two quantum wells are formed by a dilute magnetic semiconductor material (ZnMnSe) with a giant Zeeman splitting of the conduction band is theoretically investigated. Self-consistent numerical simulations of the structure predict giant magnetocurrent in the resonant bias regime as well as significant current spin polarization for a considerable range of applied biases.Comment: 4 pages, 4 figure

Graphene on transition-metal dichalcogenides: a platform for proximity spin-orbit physics and optospintronics

Hybrids of graphene and two dimensional transition metal dichalcogenides (TMDC) have the potential to bring graphene spintronics to the next level. As we show here by performing first-principles calculations of graphene on monolayer MoS$_2$, there are several advantages of such hybrids over pristine graphene. First, Dirac electrons in graphene exhibit a giant global proximity spin-orbit coupling, without compromising the semimetallic character of the whole system at zero field. Remarkably, these spin-orbit effects can be very accurately described by a simple effective Hamiltonian. Second, the Fermi level can be tuned by a transverse electric field to cross the MoS$_2$ conduction band, creating a system of coupled massive and massles electron gases. Both charge and spin transport in such systems should be unique. Finally, we propose to use graphene/TMDC structures as a platform for optospintronics, in particular for optical spin injection into graphene and for studying spin transfer between TMDC and graphene.Comment: 7 pages, 6 figure

Spin switch and spin amplifier: magnetic bipolar transistor in the saturation regime

It is shown that magnetic bipolar transistors (MBT) can amplify currents even in the saturation regime, in which both the emitter-base and collector-base junctions are forward biased. The collector current and the current gain can change sign as they depend on the relative orientation of the equilibrium spin in the base and on the nonequilibrium spin in the emitter and collector. The predicted phenomena should be useful for electrical detection of nonequilibrium spins in semiconductors, as well as for magnetic control of current amplification and for current switching.Comment: 5 pages, 4 figures; paper to a presentation at XXXIII International School on the Physics of Semiconductor Compounds Jaszowiec 200

Theory of anisotropic exchange in laterally coupled quantum dots

The effects of spin-orbit coupling on the two-electron spectra in lateral coupled quantum dots are investigated analytically and numerically. It is demonstrated that in the absence of magnetic field the exchange interaction is practically unaffected by spin-orbit coupling, for any interdot coupling, boosting prospects for spin-based quantum computing. The anisotropic exchange appears at finite magnetic fields. A numerically accurate effective spin Hamiltonian for modeling spin-orbit-induced two-electron spin dynamics in the presence of magnetic field is proposed.Comment: 4 pages, 3 figures; paper rewritte

Self-sustained magnetoelectric oscillations in magnetic resonant tunneling structures

The dynamic interplay of transport, electrostatic, and magnetic effects in the resonant tunneling through ferromagnetic quantum wells is theoretically investigated. It is shown that the carrier-mediated magnetic order in the ferromagnetic region not only induces, but also takes part in intrinsic, robust, and sustainable high-frequency current oscillations over a large window of nominally steady bias voltages. This phenomenon could spawn a new class of quantum electronic devices based on ferromagnetic semiconductors.Comment: 5 pages, 4 figure

Spin relaxation mechanism in graphene: resonant scattering by magnetic impurities

It is proposed that the observed small (100 ps) spin relaxation time in graphene is due to resonant scattering by local magnetic moments. At resonances, magnetic moments behave as spin hot spots: the spin-flip scattering rates are as large as the spin-conserving ones, as long as the exchange interaction is greater than the resonance width. Smearing of the resonance peaks by the presence of electron-hole puddles gives quantitative agreement with experiment, for about 1 ppm of local moments. While the local moments can come from a variety of sources, we specifically focus on hydrogen adatoms. We perform first-principles supercell calculations and introduce an effective Hamiltonian to obtain realistic input parameters for our mechanism.Comment: 5 pages, 3 figures + Suppl. material (3 pages, 5 figures