Alpha particle induced switching in Josephson tunnel junctions

Alpha particle irradiation has been observed to cause Josephson tunnel junctions to switch from the zero resistance to the finite resistance state. The results can be interpreted by assuming that a portion of the junction is raised above Tcby the energy lost by the alpha particle as it passes through or near the device. This causes a redistribution of the current to the portion of the device which is still superconducting, and an upset will then occur if the critical current density is exceeded. The data indicates that every alpha particle that can raise a sufficiently large area above Tcwill cause an upset. For the Nb-Si-Nb devices studied here, an alpha incident at 90 degrees to the plane of a junction will "normalize" an area of about 1.3 square micrometers if it deposits energy at a rate of 350 keV per micrometer along its track.