Conductance Oscillations in Spin Field-Effect Transistors

Ballistic spin transport in spin field-effect transistors is studied by taking into account the Rashba spin-orbit coupling, interfacial scattering, and band mismatch. It is shown that thespin conductance oscillation with the semiconductor channel length is a superimposition of the Rashba spin precession and spin interference oscillations. They have different oscillation periods π/k_R and π/k with k_R the Rashbawavevector and k the Fermi wavevector of the semiconductor channel,and play different parts of slow and rapid oscillations, depending upon therelative magnitude of π/k_R and π/k. Only atk=k_R does the spin conductance exhibit oscillations of a single period. Two types of different behaviors of the tunnelling magnetoresistance are discussed.