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arXiv · 1510.06440

Microwave photon-assisted phase-incoherent Cooper-pair tunneling in a Josephson STM

A. Roychowdhury·M. Dreyer·J. R. Anderson·C. J. Lobb·F. C. Wellstood
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Abstract

We have observed photon-assisted Cooper-pair tunneling in an atomic-scale Josephson junction formed between a superconducting Nb tip and a superconducting Nb sample in a scanning tunneling microscope (STM) at 30 mK. High-resolution tunneling spectroscopy data show a zero-bias conduction peak and other sharp sub-gap peaks from coupling of the STM junction to resonances in the electromagnetic environment. The sub-gap peaks respond to incident microwave radiation by splitting into multiple peaks with the position and height depending on the frequency and amplitude of the microwaves. The inter-peak spacing shows that the charge carriers are Cooper pairs, rather than quasiparticles, and the power dependence reveals that the current originates from photon-assisted phase-incoherent tunneling of pairs, rather than the more conventional phase-coherent tunneling of pairs that yields Shapiro steps.

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A. Roychowdhury, M. Dreyer, J. R. Anderson, C. J. Lobb, F. C. Wellstood. 2015-10-21. Microwave photon-assisted phase-incoherent Cooper-pair tunneling in a Josephson STM. https://doi.org/10.1103/physrevapplied.4.034011

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