Spin transport in multiterminal devices: Large spin signals in devices with confined geometry

We propose a general analytical theory based on the transfer-matrix formalism to describe the spin transport in multiterminal lateral devices with metallic, semiconducting, or carbon-based conducting channels. Our theory expresses local and nonlocal spin resistances as a function of components of the transfer matrices. An important result for practical devices is the prediction that confined geometries can give much larger spin signals than those of the already known standard situation.