Current-Phase Relationship of Josephson Junctions with Nb_xSi_1-x Barriers

We characterized the current-phase relationship (CΦR) of Josephson junctions with niobium doped amorphous silicon barriers. We performed an indirect measurement of the CΦR by incorporating the test junction into an RF-SQUID inductively coupled to a DC-SQUID magnetometer. We observed deviations from the typical sinusoidal relationship. This non-sinusoidal CΦR also causes non-integer Shapiro steps. We measured both SIS and SNS junctions and observed the CΦR changing with barrier composition. Additionally, non-sinusoidal CΦR can be observed in high-current-density junctions used for mixed-signal and microwave circuits. Understanding the CΦR and its effects on junction behavior is necessary for accurate modeling, such as that required by the IARPA-SuperTools program. These intrinsically shunted Josephson junctions are particularly useful for applications requiring high junction density, such as superconducting computing and waveform synthesis. More accurate junction models will enable higher performance of large-scale superconductive circuits.