Quasiparticle excitation in a superconducting tunnel junction byαparticles

The electric signals induced by $\alpha$ particles in an $S-I-S$ tunnel junction of Sn were measured in the temperature region of 1.37-4.2 K. From the pulse-height dependence on the electric current through the junction and on temperature, it was found that the impulsive change in the current-voltage ($I-V$) characteristics in the sample cannot be explained simply by the localized superconducting-normal transition due to the temperature increase. By adopting a simple model, however, it has been revealed that excess quasiparticles are essential to the characteristic change in the junction.