Charging in Solitary, Voltage Biased Tunnel Junctions

We present experiments together with a phenomenological model on the zero bias anomaly of a single, voltage biased normal metal $(\mathrm{Al}/{\mathrm{AlO}}_x/\mathrm{Al})$ tunnel junction, and conclude, based on clearcut results in the high temperature regime, that this resistance peak is determined purely by the charging effect. The capacitance to be charged is, however, increased over the junction capacitance by the connecting leads within the “horizon” of the tunnel junction.