High-Supercurrent-Density Contacts and Josephson Effect of Strontium Ruthenate

摘要

We have developed a process of fabricating high-supercurrent-density contacts to Sr_2RuO_4 as a key technology for the development of topological quantum computing. To minimize degradation, the niobium contacts were formed on crushed surfaces of Sr_2RuO_4 crystals by an in situ process. A critical supercurrent density as high as 10~7 A/m~2 was achieved, a value two to three orders of magnitude greater than those reported previously. However, the unexpectedly small magnitude of the product of the critical current and the normal resistance indicates the existence of a fundamental limitation arising from Josephson coupling between spin-singlet and spin-triplet superconductivities.