Toward realization of novel superconductivity based on twisted van der Waals Josephson junction in cuprates
일 시 : 2022년 05월 24일 화요일 13:00
연 사 : 김 필 립 교수 (Harvard University)
장 소 : 자연과학관 224호
초 록
Twisted interfaces between stacked van der Waals cuprate crystals enable tunable Josephson coupling, utilizing anisotropic superconducting order parameters. Employing a novel cryogenic assembly technique, we fabricate high-temperature Josephson junctions with an atomically sharp twisted interface between Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ crystals. The critical current density $J_c$ sensitively depends on the twist angle. While near 0$^\circ$ twist, $J_c$ nearly matches that of intrinsic junctions, it is suppressed almost 2-orders of magnitude but remained finite near 45$^\circ$. $J_c$ also exhibits non-monotonic behavior \textit{vs} temperature due to competition between two supercurrent contributions from nodal and anti-nodal regions of the Fermi surface. Near $45^\circ$ twist angle, we observe two-period Fraunhofer interference patterns and fractional Shapiro steps at half integer values, a signature of co-tunneling Cooper pairs necessary for high temperature topological superconductivity.