TRANSPORT-PROPERTIES OF A QUANTUM-DOT WITH SUPERCONDUCTING LEADS

We report a numerical study of transport properties of a quantum dot w ith superconducting leads. We introduce a general phenomenological mod el of quantum-dot transport, in which electron tunnel rates are comput ed within the Fermi-golden-rule approach. The low-temperature current- voltage (I-V) characteristics are in qualitative agreement with experi mental observations of Ralph et al. [Phys. Rev. Lett. 74, 3241 (1995)] . At higher temperatures, our results reveal interesting effects due t o the thermal excitation of quasiparticles in the leads as well as the thermal population of excited quantum levels in the dot. We also stud y the photon-assisted tunneling phenomena in our system and point out its potential for millimeter wave applications.