Finite-bias resistance peaks in nanoscale superconductor-normal-metal Ta-Wpoint contacts

High resistance (10-1000 Omega) ballistic nanoconstrictions were formed bet ween bulk superconducting tantalum and an electrochemically sharpened (10-2 00 nm radius at tip) tungsten whisker. Measurements of the dynamic resistan ce of these contacts showed resistance peaks at symmetric voltages sizeably larger than the superconducting gap (\V\ > 10 Delta). The voltage at which these peaks occur was found to be linear in the square root of the measure d contact resistance, strongly supporting a model in which the resistance p eaks result from the destruction of superconductivity by the magnetic held produced by current flow. through the contact. The model is in quantitative agreement with observation and implies that each resistance peak correspon ds to the appearance of a single Burr quantum around the current flowing th rough the contact.