Mahdi Zarea

Electron-Electron and Spin-Orbit Interactions in Armchair Graphene Ribbons

The effects of intrinsic spin-orbit and Coulomb interactions on low-energy properties of finite width graphene armchair ribbons are studied by means of a Dirac Hamiltonian. It is shown that metallic states subsist in the presence of intrinsic spin-orbit interactions as spin-filtered edge states, in contrast with the insulating behavior predicted for graphene planes. A charge-gap opens due to Coulomb interactions in neutral ribbons, that vanishes as Delta approximately 1/W, with a gapless spin sector. Weak intrinsic spin-orbit interactions do not change the insulating behavior. Explicit expressions for the width-dependent gap and various correlation functions are presented.

Enhancement of the Kondo effect through Rashba spin-orbit interactions.

We study a one-orbital Anderson impurity in a two-dimensional electron bath with Rashba spin-orbit interactions in the Kondo regime. The spin SU(2) symmetry-breaking term couples the impurity to a two-band electron gas. A Schrieffer-Wolff transformation shows the existence of the Dzyaloshinsky-Moriya interaction away from the particle-hole symmetric impurity state. A renormalization group analysis reveals a two-channel Kondo model with ferro- and antiferromagnetic couplings. The parity-breaking Dzyaloshinsky-Moriya term renormalizes the antiferromagnetic Kondo coupling with an exponential enhancement of the Kondo temperature.

Spin Hall effect in two-dimensional p-type semiconductors in a magnetic field

We calculate the spin Hall conductivity driven by Rashba spin-orbit interaction in

Landau level mixing by full spin-orbit interactions

p

Unscreened Coulomb interactions and the quantum spin Hall phase in neutral zigzag graphene ribbons.

-type two-dimensional semiconductors in the presence of a perpendicular magnetic field. For a highly confined quantum well, the system is described by a

Graphene zigzag ribbons, square lattice models and quantum spin chains

k

Quantum spin Hall phase in neutral zigzag graphene ribbons

-cubic Rashba term for two-dimensional heavy holes. The eigenstates of the system can be described by Landau spinor states. First we consider the conventional spin Hall conductivity. The contribution of the interband transitions to the Kubo-Greenwood formula gives the density dependent intrinsic spin Hall conductivity, which approaches its universal value

Rash spin-orbit interaction in graphene and graphene zigzag nano-ribbons

{\ensuremath{\sigma}}_{xy}^{z}=9e∕8\ensuremath{\pi}

Rashba spin-orbit interaction in graphene and zigzag nanoribbons

for weak spin-orbit coupling and low Fermi energies, in agreement with previous work. However two intraband contribution terms cancel this effect leading to zero conventional spin Hall conductivity. Adding the torque dipole contribution to the definition of spin current, we also study the effective spin conductivity. This is shown to be proportional to the total magnetization plus surface terms which exactly cancel it for small spin-orbit coupling. If in low magnetic field the intraband transitions evolve to vertex corrections, the fact that both effective and conventional spin Hall conductivities vanish is unexpected. This suggests that the zero magnetic field limit of the model is singular.

Influence of Rashba spin-orbit interactions on the Kondo effect

The manipulation of the spin of charge carriers in semiconductors, spintronics, has attracted increasing interest in recent years. In the paradigmatic Datta-Das spin transistor, 1 the spin of the electron passing through the device is controlled by the Rashba spin-orbit (SO) interaction, 2 which in turn can be varied by the application of gate voltages. The Rashba interaction stems from the structural inversion asymmetry (SIA) introduced by a heterojunction or by surface or external fields. In semiconductors with narrower energy gap (InGaAs, AlGaAs), this effect is expected to be stronger. It has been shown experimentally that the Rashba spin-orbit interaction can be modified up to 50% by external gate voltages. 3,4 In addition to the Rashba coupling there is also a material-intrinsic Dresselhaus spin-orbit interaction. This originates from the bulk inversion asymmetry (BIA) of the crystal, and can be relatively large in semiconductors like InSb/InAlSb. 5