Theory of correlated electron transport and inelastic tunneling spectroscopy

For a non-superconducting system, the electronic tunneling current through an insulating barrier is calculated, including interaction effects. The exact Hamiltonian of the full system is projected onto the subspaces of the "left" and "right" leads. In the weak tunneling limit the well-known tunneling Hamiltonian is recovered, along with an additional term. This additional term originates from the projection of the electron-electron interaction onto each subsystem and corresponds to correlated tunneling. It is shown that the tunneling current is determined by---in addition to the single-particle density of states---the spin-spin and density-density susceptibilities. The signatures of which have recently been observed in several experiments.