Time-resolved quantum transport of charge in a nano-structured chain of superconducting tunnel junctions

by Tim Duty (University of New South Wales)

Wednesday 21 May 2014, 15:00 → 16:00 Europe/Stockholm

Nordita West (122:026)

At low temperatures and large charging energies, arrays of sub-micron superconducting tunnel junctions are usually depicted as a realization of the disordered Bose-Hubbard model, where individual Cooper pairs hop from island to island via Josephson tunneling. On the other hand, normal metal junction arrays are thought to be adequately described by the so-called Orthodox Theory of single electron tunneling, which is based on Fermi’s Golden Rule. For 1D chains the latter theory predicts charge transport due to time-correlated tunneling of a train of electrons. Such current-to-frequency conversion, although stochastic in nature, is reminiscent of voltage-to-frequency conversion that occurs in the Josephson effect and consequently has metrological significance. I will present new experimental results for a 50 island chain of junctions that combine femtoamp current measurement with local charge sensing at MHz bandwidths using a radio-frequency single-charge transistor. This allows us to observe, somewhat surprisingly, what appears to be single-electron tunneling in the superconducting regime, which is conspicuously absent in the normal state presumably due to offset charge disorder. Charge transport in the array is thermally activated and uncorrelated at higher temperatures, but saturates at low temperatures where robust time correlation is observed