Magnetically enhanced terahertz response of Josephson junctions

We investigate the magnetic field effects on the terahertz (THz) response of grain boundary Josephson junctions. First, we show some experimental results of the THz response enhanced by a dc magnetic field. The experimental results and device configuration indicate that the THz RF magnetic field plays a role in enhancing the response. Second, we numerically simulate the current-voltage characteristics and obtain the power dependence of Shapiro steps. Since the junctions are wide compared to the inferred Josephson penetration depth, multiple current paths within a junction are possible and superconducting quantum interference device (SQUID) models should be used. Two kinds of SQUID models are used: an RF-current drive model and an RF-field activation model. Shapiro step enhancement by a dc magnetic field can be reproduced with the use of the RF-field activation model. Finally, we discuss step-height dependence on SQUID parameters as well as give a qualitative explanation for the different predictions of two SQUID models.