Abstract
Using the nonequilibrium Green function, we show that microwave irradiation can reverse the supercurrent flowing through a superconductor/quantum dot/superconductor structure. In contrast with the conventional sideband effect in normal-metal/quantum dot/normal-metal junctions, the photon-assisted structures appear near where is the resonant energy level of the quantum dot and ω is the frequency of microwave field. Each photon-assisted structure is composed of a negative and a positive peak, with an abrupt jump from the negative peak to the positive peak around The microwave-induced π-junction transition is interpreted in the picture of photon-assisted Andreev bound states, which are formed due to multiple photon-assisted Andreev reflection between the two superconductors. Moreover, the main resonance located at can also be reversed with proper microwave strength and frequency.
- Received 1 April 2002
DOI:https://doi.org/10.1103/PhysRevB.66.134507
©2002 American Physical Society