Ballistic spin transport in a two-dimensional electron gas

We explore electrically injected, spin-polarized transport in a ballistic two-dimensional electron gas. We augment the B\"uttiker-Landauer picture with a simple, but realistic model for spin-selective contacts to describe multimode reservoir-to-reservoir transport of ballistic spin-1/2 particles. Clear and unambiguous signatures of spin transport are established in this regime, for the simplest measurement configuration that demonstrates them directly. These effects originate from spin precession of ballistic carriers; they exhibit a strong dependence upon device geometry, and vanish in the diffusive limit. Our results have important implications for prospective ``spin transistor'' devices.