Tunable Cooper quartet transport and Josephson diode effect in 1T-PtTe₂ Josephson junctions

Supercurrent diode effects have recently attracted much attention due to their potential applications in superconducting logic circuits and the study of fundamental symmetries in the superconducting state. In this work, we establish the presence of a large Josephson diode effect (JDE) in lateral Josephson junctions formed from a van der Waals type-II Dirac semimetal 1T-PtTe₂. A second-order current phase relationship model is used to simulate the measured JDE, which indicates that the JDE is proportional to the phase difference between the first (Cooper pair) and second-order (Cooper quartet) supercurrents in the junction. Measurements of the JDE as a function of the in-plane magnetic field and the flux through the junction are shown to agree with the predictions, indicating the presence of large second harmonic supercurrents in the junction. Moreover, half-flux quantum oscillations are observed in JDE, demonstrating the pure second-order nature of the observed JDE. The measured transparencies of the PtTe₂ junctions indicate that the contribution of the Meissner screening currents to the JDE is small compared to the observed efficiencies, indicating the strong role of helical spin-momentum locking in the creation of JDE. The high chemical stability along with the strong Josephson coupling provided by PtTe₂, make it an ideal platform to further investigate JDE and pure Cooper quartet transport effects in Josephson junctions.