Current conservation in two-dimensional ac transport

The electric current conservation in a two-dimensional quantum wire under a time-dependent field is investigated. Such a conservation is obtained as the global density of states contribution to the emittance is balanced by the contribution due to the internal charge response inside the sample. However when the global partial density of states is approximately calculated using scattering matrix only, correction terms an needed to obtain precise current conservation. We have derived these corrections analytically using a specific two-dimensional system. We found that when the incident energy E is near the first subband, our result reduces to the one-dimensional result. As E approaches to the nth subband with n > 1, the correction term diverges. This explains the systematic deviation to precise current conservation observed in a previous numerical calculation.