Anomalous Pumped and Unpumped I-V Characteristics of Nb SIS Terahertz Mixers with NbTiN Striplines

To achieve nearly quantum limited noise temperatures around 1 THz in Nb SIS mixers NbTiN is used as stripline material because its high DC conductivity and gap frequency above 1 THz should minimize RF losses. However, one expects problems at the Nb/NbTiN interface due to an energy gap discontinuity. Indeed, the measured I-V curves show features that are… (More)