Zeeman-split mesoscopic transport through a normal-metal–quantum-dot–superconductor system with ac response

Abstract

We have investigated the Zeeman-split mesoscopic transport through the normal-metal--quantum-dot--superconductor system applied with a microwave field. We employ BCS theory to describe the Hamiltonian of the superconducting lead. The time-averaged tunneling current formula is derived by using the Keldysh's nonequilibrium Green-function technique in the Nambu representation. The multilevel quantum dot is considered for the noninteraction system in the calculations. The spin split Andreev reflection and photon-electron pumping behaviors are investigated in the presence of a Zeeman magnetic field. The resonant structure versus Zeeman energy and gate voltage is revealed. The Zeeman-split photon-assisted I-$V$ characteristics are evaluated for the single-channel quantum-dot system. By adjusting the Zeeman magnetic field, we can obtain a large resonant tunneling current even if in the Andreev reflection regime. The current appears to have interesting structures versus Zeeman energy for the multichannel quantum-dot system associated with a different gate voltage. The negative and positive current appear in the symmetric forms by controlling the Zeeman field.