Excess Kondo resonance in a quantum dot device with normal and superconducting leads: the physics of Andreev-normal co-tunneling

摘要

We report on a novel Kondo phenomenon of interacting quantum dots coupledasymmetrically to a normal and a superconducting lead. The effects of intradotCoulomb interaction and Andreev tunneling give rise to Andreev boundresonances. As a result, a new type of co-tunneling process which we termAndreev-normal co-tunneling, is predicted. At low temperatures, coherentsuperposition of these co-tunneling processes induces a Kondo effect in whichCooper pairs directly participate formation of a spin singlet, leading to fourKondo resonance peaks in the local density of states, and enhancing thetunneling current.