Ballistic transport and spin dependent anomalous quantum tunnelling in Rashba-Zeeman and bilayer graphene hybrid structures (original) (raw)

Chiral tunneling in single-layer graphene with Rashba spin-orbit coupling: Spin currents

Physical Review B

We study 1D barrier penetration of 2D massless Dirac electrons in single layer graphene in the presence of uniform Rashba spin-orbit coupling, thereby exploring the role Klein paradox in graphene spintronics. Spin density and spin-current density are calculated (in addition to transmission), and shown to be remarkably different from those predicted in bulk single layer graphene. In particular, they are rather sensitive to the strength of the spin-orbit coupling and the height of the potential barrier, and have a non-trivial space dependence (associated with spin torque). Such a system may serve as a graphene based spintronic device without the use of an external magnetic field or magnetic materials.

Spin-dependent electron transport in graphene junctions in the presence of Rashba spin-orbit interaction

Journal of Applied Physics, 2012

In this Letter, the authors study the effects of electrostatic potential on spin-inversion properties in nano-scale graphene sheets with a single Rashba spin-orbit barrier using the transfer matrix method. The optimum values of the Rashba constant are obtained for maximum electron spin-inversion. It is found that, in the presence of electrostatic potential, perfect spin-inversion can take place for all values of the electron incident angle, whereas in the absence of electrostatic potential, perfect spin-inversion can take place only at specific values of electron incident angle. The spin-dependent electron conductance as well as the efficiency of graphene spin-inverter increase in the presence of electrostatic potential.

The role of the Rashba coupling in spin-current of monolayer gapped graphene

The European Physical Journal B, 2014

In the current work we have investigated the influence of the Rashba spin-orbit coupling on spin-current of a single layer gapped graphene. It was shown that the Rashba coupling has a considerable role in generation of the spin-current of vertical spins in mono-layer graphene. The behavior of the spincurrent is determined by density of impurities. It was also shown that the spin-current of the system could increase by increasing the Rashba coupling strength and band-gap of the graphene and the sign of the spin-current could be controlled by the direction of the current-driving electric field.

Spin-inversion in nanoscale graphene sheets with a Rashba spin-orbit barrier

Spin-inversion properties of an electron in nanoscale graphene sheets with a Rashba spin-orbit barrier is studied using transfer matrix method. It is found that for proper values of Rashba spin-orbit strength, perfect spin-inversion can occur in a wide range of electron incident angle near the normal incident. In this case, the graphene sheet with Rashba spin-orbit barrier can be considered as an electron spin-inverter. The efficiency of spin-inverter can increase up to a very high value by increasing the length of Rashba spin-orbit barrier. The effect of intrinsic spin-orbit interaction on electron spin inversion is then studied. It is shown that the efficiency of spin-inverter decreases slightly in the presence of intrinsic spin-orbit interaction. The present study can be used to design graphene-based spintronic devices.

Rashba coupling induced spin susceptibility and magnetic phase transition of conduction electrons in monolayer graphene

Physica E: Low-dimensional Systems and Nanostructures, 2015

Using the Kubo formalism, the magnetic properties of the system in the linear regime have been investigated. Mainly the effect of non-magnetic substrate on the spin susceptibility is calculated. Results show that the Rashba coupling interaction has a central role in the magnetic response function of the system and it is really remarkable since this type of spin orbit coupling can be effectively controlled by an external gate voltage. Most importantly it was shown that, in the presence of the Rashba interaction a magnetic phase transition could be observed. This magnetic phase corresponds to a magnetic order of conduction electrons that takes place at some especial frequency of external magnetic field.

Spin-polarized current and tunneling magnetoresistance in ferromagnetic gate bilayer graphene structures

Journal of Applied Physics, 2011

We study spin transport in bilayer graphene structures where gate electrodes are attached to ferromagnetic graphene. Due to the exchange field in the gated regions, the current becomes spin dependent and can be controlled by tuning the gate voltages. It is shown that thanks to strong resonant chiral tunneling inherent in bilayer graphene, very high spin polarization and tunneling magnetoresistance can be achieved in the considered structures. Different possibilities for controlling the spin current are discussed. The study demonstrates the potential of bilayer graphene structures for spintronic applications with significant improvement over previously predicted results in monolayer graphene structures.

Transverse Spin Transport in Graphene

International Journal of Modern Physics B, 2009

In this paper we report transverse spin transport properties of graphene in a device, where for the first time a mono-atomically thin atomic fabric was sandwiched between magnetic thin films. We found that a single layer graphene flake was sufficient to break the exchange coupling between magnetic films and also to enhance the magnetoresistance effect.

Controlled engineering of spin-polarized transport properties in a zigzag graphene nanojunction

EPL (Europhysics Letters)

We investigate a novel way to manipulate the spin polarized transmission in a two terminal zigzag graphene nanoribbon in presence of Rashba spin-orbit (SO) interaction with circular shaped cavity engraved into it. A usual technique to control the spin polarized transport behaviour of a nanoribbon can be achieved by tuning the strength of the SO coupling, while we show that an efficient engineering of the spin polarized transport properties can also be done via cavities of different radii engraved in the nanoribbon. Simplicity of the technique in creating such cavities in the experiments renders an additional handle to explore transport properties as a function of the location of the cavity in the nanoribbon. Further, a systematic assessment of the interplay of the Rashba interaction and the dimensions of the nanoribbon is presented. These results should provide useful input to the spintronic behaviour of such devices. In addition to the spin polarization, we have also included an interesting discussion on the charge transmission properties of the nanoribbon, where, in absence of any SO interaction a metal-insulator transition induced by the presence of a cavity is observed.