Theory of tunneling processes in quantum structures

A theoretical framework to build a concrete analysis method for tunneling p rocesses through quantum structures (QSs) is proposed based on Keldysh Gree n's function. As a result of three steps of transformations, we deduce the general expression for the current flowing through QSs which corresponds to the nonequilibrium and the nonlinear version of the Kubo formula. It is re vealed how we can achieve the general formula successfully. It is shown tha t. in tunneling processes through QSs, both the elastic scattering and the inelastic scattering play an essential role. Our framework is expected to b e applicable to various QSs fabricated by metals, semiconductors, supercond uctors and magnetic materials, since our procedure is not sensitive to deta ils of the Hamiltonian.