  Current-induced spin polarization (CISP) is rederived in ballistic
spin-orbit-coupled electron systems, based on equilibrium statistical
mechanics. A simple and useful picture is correspondingly proposed to help
understand the CISP and predict the polarization direction. Nonequilibrium
Landauer-Keldysh formalism is applied to demonstrate the validity of the
statistical picture, taking the linear Rashba-Dresselhaus [001] two-dimensional
system as a specific example. Spin densities induced by the CISP in
semiconductor heterostructures and in metallic surface states are compared,
showing that the CISP increases with the spin splitting strength and hence
suggesting that the CISP should be more observable on metal and semimetal
surfaces due to the discovered strong Rashba splitting. An application of the
CISP designed to generate a spin-Hall pattern in the inplane, instead of the
out-of-plane, component is also proposed.
