Emergent Interfacial Superconductivity between Twisted Cuprate Superconductors

We developed a cryogenic assembly technique to fabricate Josephson junctions with an atomically sharp twisted interface between Bi2Sr2CaCu2O8+x crystals. We find that the Josephson critical current density $J_c$ depends sensitively on the twist angle. At small twisting angles, $J_c$ exhibits the maximum value comparable to that of the intrinsic junctions. Close to 45 degree twisting angle, $J_c$ is greatly suppressed, but it remains finite. Near 45 degree twisted angle, we observe well-developed Fraunhofer patter as well as half-integer Shapiro steps. Theoretical analysis of our data suggests that the remaining superconducting coherence at 45 degree twisted angle indicates the development of dominant second harmonic in the Josephson energy versus phase relation due to the co-tunneling of Cooper pairs, supporting time reversal symmetry broken interfacial superconductivity in this junction.