Encapsulating high-temperature superconducting twisted van der Waals heterostructures blocks detrimental effects of disorder

Abstract: High-temperature cuprate superconductors-based van der Waals (vdW) heterostructures hold high technological promise. One of the obstacles hindering progress is the detrimental effect of disorder on the properties of Josephson junctions (JJ) realized by the vdW devices. Here we report the new method of fabricating twisted vdW heterostructures made of Bi2Sr2CuCa2O8+d, crucially improving the JJ characteristics, pushing them up to those of the intrinsic JJs in bulk samples. The method combines a cryogenic stacking using a solvent-free stencil mask technique and covering interface by the insulating hexagonal boron nitride crystals. Despite the high-vacuum condition down to 10-6 mbar in the evaporation chamber, the interface appears to be protected from water molecules during the in-situ metal deposition only when fully encapsulated. Comparing the current-voltage curves of encapsulated and unencapsulated interfaces, we reveal that the encapsulated interfaces' characteristics are crucially improved so that the corresponding JJs demonstrate high critical currents and sharpness of the superconducting transition comparable to those of the intrinsic JJs. Finally, we show that the encapsulated heterostructures are more stable in time.