Differential Conductance Anomaly in Superconducting Quantum Point Contacts

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We present in this letter a theoretical analysis of the current-voltage (I-V) characteristics of a hybrid normal-superconducting device consisting of a quantum dot and two electrodes that can be either normal or superconducting. We show that voltage drops at two different contacts that have been regarded unimportant in literature play essential roles in the Andreev tunneling process when at least one of electrodes is superconducting. A differential-conductance-anomaly caused by the aforementioned voltage drops is predicted. We also propose a new spectroscopy method to measure the energy levels of a quantum dot as well as voltage drops at contacts between the quantum dot and the two leads. Our findings have potential applications for the next generation of electronic devices at nanoscale.