  Quantum wires with periodic local Rashba spin-orbit couplings are proposed
for a higher performance of spin field-effect transistor. Fano-Rashba quantum
interference due to the spin-dependent modulated structure gives rise to a
broad energy range of vanishingly small transmission. Tuning Rashba spin-orbit
couplings can provide the on- or off-currents with extremely large on/off
current ratios even in the presence of a strong disorder.
