Persistent Josephson tunneling between Bi2Sr2CaCu2O8+x flakes twisted by

Yuying Zhu,Heng Wang, Z. G. Wang,Shuxu Hu,Genda Gu,Jing Zhu,Ding Zhang,Qi‐Kun Xue

There is an on-going debate on the pairing symmetry -- whether it is $s$-, $d$-, or $d+i\phantom{\rule{0}{0ex}}d$-wave -- in twisted cuprates. Here, the authors obtain strong Josephson tunneling in 45${}^{\ensuremath{\circ}}$-twisted cuprates with ultrahigh interfacial quality and precisely calibrated twist angles. The results firmly establish the existence of isotropic pairing in twisted cuprates, posing strong constraints on the theory considering a pure $d$ wave or $d+i\phantom{\rule{0}{0ex}}d$ wave. They also extend the study to the overdoped regime and observe the Josephson diode effect, promising next-generation high-temperature superconducting devices.