Anisotropic spin and charge transport in Rashba Hamiltonian .

We explore spin and charge transport phenomena in two dimensional electron gas in presence of Rashba spin-orbit coupling connected to two ideal Ferromagnetic leads. In particular we show through a combination of analytical and numerical calculation that the spin polarization which is transported depends on the Magnetization direction of ferromagnet even if the magneti-zation of both FM's are parallel.Conductance is also shown to be anisotropic. These anisotrpies present in spin and charge transport are a consequence of breaking of rotational invariance due to Rashba spin-orbit interaction and are present irrespective of the Hamiltonian considered being an effective mass Hamiltonian or tight binding model Hamiltonian. The growing field of spintronics has attracted a lot of interest after the proposal of spin-filed effect transistor (SPIN-FET) by Datta and Das [1]. The Datta-Das SPIN-FET is a hybrid structure of type FM1-2DEG-FM2, where 2DEG is a two-dimensional electron gas of a narrow gap semiconductor (InAS) and FM1 and FM2 are injector and detector Fer-romagnetic contacts. The working of this device relies on the manipulation of electronic spin state in 2DEG with the electric field of an external gate electrode. Essential for this mechanism is field dependent spin-orbit coupling, which is relatively large and well established [2]. It is now generally accepted that the spin-orbit coupling in narrow-gap 2DEG is governed by Rashba Hamiltonian [3]. For a 2DEG lying in xy plane(see Fig.1) the Rashba spin-orbit interaction has the form, H R = α(k × σ) · ˆ z,with k being momentum vector, σ