  Twisted interfaces between stacked van der Waals cuprate crystals enable
tunable Josephson coupling between in-plane anisotropic superconducting order
parameters. Employing a novel cryogenic assembly technique, we fabricate
Josephson junctions with an atomically sharp twisted interface between
Bi2Sr2CaCu2O8+x crystals. The Josephson critical current density sensitively
depends on the twist angle, reaching the maximum value comparable to that of
the intrinsic junctions at small twisting angles, and is suppressed by almost 2
orders of magnitude yet remains finite close to 45 degree twist angle. Through
the observation of fractional Shapiro steps and the analysis of Fraunhofer
patterns we show that the remaining superconducting coherence near 45 degree is
due to the co-tunneling of Cooper pairs, a necessary ingredient for
high-temperature topological superconductivity.
