We report on a new experimental approach to the size estimation of the hot spot induced by ionizing particles in a Josephson tunnel junction. Here, in contrast to the case of a superconducting strip, it is possible to investigate the hot spot dynamics in absence of effects due to the heating induced by the bias current. The reported experiment is based on the motion of Abrikosov vortices, trapped in the thin films constituting the junction electrodes, under 5.6 MeV α-particle irradiation. The fast time evolution of a hot spot, combined with the presence of Abrikosov vortices, produces a change of the static magnetic field in the junction area and thus a change of the critical current value, Ic. Measurements of Ic during the α-particle irradiation and in presence of trapped Abrikosov vortices allow to determine the rate of appearance of those Ic changes. The behavior of the average appearance rate as function of the Abrikosov vortices density provides a direct determination of the maximum hot spot area. The experiment is performed on a high quality Nb/Al–AlOx/Nb junction of circular geometry and with “small” dimensions with respect to the Josephson penetration depth. A value of 4.7±1.2 μm2 is found for the maximum hot spot area. © 1997 American Institute of Physics.

Experimental estimation of the hot spot size in Nb-based Josephson tunnel junctions using Abrikosov vortices

PAGANO, Sergio;
1997-01-01

Abstract

We report on a new experimental approach to the size estimation of the hot spot induced by ionizing particles in a Josephson tunnel junction. Here, in contrast to the case of a superconducting strip, it is possible to investigate the hot spot dynamics in absence of effects due to the heating induced by the bias current. The reported experiment is based on the motion of Abrikosov vortices, trapped in the thin films constituting the junction electrodes, under 5.6 MeV α-particle irradiation. The fast time evolution of a hot spot, combined with the presence of Abrikosov vortices, produces a change of the static magnetic field in the junction area and thus a change of the critical current value, Ic. Measurements of Ic during the α-particle irradiation and in presence of trapped Abrikosov vortices allow to determine the rate of appearance of those Ic changes. The behavior of the average appearance rate as function of the Abrikosov vortices density provides a direct determination of the maximum hot spot area. The experiment is performed on a high quality Nb/Al–AlOx/Nb junction of circular geometry and with “small” dimensions with respect to the Josephson penetration depth. A value of 4.7±1.2 μm2 is found for the maximum hot spot area. © 1997 American Institute of Physics.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11386/3196479
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