Long-range phase coherence and tunable second order φ0-Josephson effect in a Dirac semimetal 1T-PtTe2

Superconducting diode effects have recently attracted much attention for their potential applications in superconducting logic circuits. Several pathways have been proposed to give rise to non-reciprocal critical currents in various superconductors and Josephson junctions. In this work, we establish the presence of a large Josephson diode effect in a type-II Dirac semimetal 1T-PtTe2 facilitated by its helical spin-momentum locking and distinguish it from extrinsic geometric effects. The magnitude of the Josephson diode effect is shown to be directly correlated to the large second-harmonic component of the supercurrent. We denote such junctions, where the relative phase between the two harmonics can be tuned by a magnetic field, as ‘tunable second order φ0-junctions’. The direct correspondence between the second harmonic supercurrents and the diode effect in 1T-PtTe2 junctions at relatively low magnetic fields makes it an ideal platform to study the Josephson diode effect and Cooper quartet transport in Josephson junctions. This work reports on the observation of a large Josephson diode effect in a type-II Dirac semimetal 1T-PtTe2. The magnitude of the Josephson diode effect is found to be related to an asymmetry of the critical supercurrent which is modeled as a phase shift between the first and second harmonic terms of the current-phase relationship and can be tuned by an external magnetic field.