Low-temperature scanning electron microscopy of niobium superconducting tunnel junctions with trapping blocks

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Abstract
In this paper we investigate the QP transport and loss mechanisms in a superconducting tunnel junction using the Low Temperature Scanning Electron Microscopy (LTSEM) technique. This approach allows precise control of the energy and position of a deposited electron pulse, which, within certain conditions, simulates the X-ray photo-absorption process. An Nb-Al-AlOxNb junction designed as a test structure which included Al blocks in the leads to act as quasiparticle traps, has been investigated. Asymmetries in the LTSEM signal distribution can be qualitatively described from the device geometry. From both the spatial distribution can be qualitatively described from the device geometry. From both the spatial distribution and the time resolved measurements the diffusion length in the amorphous Nb was determined to be of the order of 8 micrometers . The LTSEM technique has demonstrated that quasiparticles produced in the leads cannot enter the tunnel barrier due to the presence of the Al traps.

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