Twisted graphene-based Josephson junction detectors

This Phase I STTR will model, design, fabricate and characterize twisted graphene heterostructure Josephson junction detectors of mm-wave and THz radiation. For a range of potential Josephson junction designs, we will calculate the IV curve, the zero-magnetic-field value for the maximum zero-voltage current, the dependence of this current on rf fields and temperature, and the dynamic resistance near this current value. These quantities will enable a prediction of responsivity for broad-band detection mechanism for various device structures. We will calculate frequencies for the AC-Josephson-effect emission, which will serve as local oscillators for narrow-band heterodyne detection, the spectral purity of emission, and its power. We will fabricate Moire-patterned few layer graphene at the magic angles for superconductivity, as well as Josephson junctions based on theoretically optimized designs. The electrical properties of the fabricated Josephson junctions will be characterized down to 40 mK temperatures, and photoresponse at 15 GHz will be studied using a microstrip resonator. These Phase I theoretical and experimental efforts will inform Phase II device prototype development and characterization up to 50 GHz frequencies using existing apparatus and to THz frequencies with cryostat modifications to enable optical access.