Dynamic conductance and the scattering matrix of small conductors.

The current response to oscillating electric or magnetic fields acting on the carriers in the probes of a multichannel, multilead conductor is investigated. For a noninteracting system we find a frequency-dependent admittance matrix which is expressed in terms of scattering matrices. A self-consistent potential method is used to include Coulomb interactions. The low-frequency departure of the admittance away from the dc conductance is discussed in terms of phase-delay times and RC times