Josephson effect in twisted cuprate bicrystals

by Prof. Ding Zhang (Tsinghua University)

Wednesday 17 Apr 2024, 13:30 → 14:30 Asia/Shanghai

TDLI Meeting Room N600 (East Wing of Floor 6, North Building)

Abstract

Understanding high temperature superconductivity in cuprates requires the elucidation of their pairing symmetry. One phase-sensitive method to achieve this goal is by studying the Josephson tunneling along c-axis between two twisted cuprate superconductors. Here, we revisit the Josephson effect in c-axis twisted cuprates by employing the van der Waals stacking technique and fabricate junctions out of mechanically exfoliated thin flakes of both Bi₂Sr₂CaCu₂O_8+x (Bi-2212) [1][2] and Bi₂Sr_2-xLa_xCuO_6+y (Bi-2201) [3]. In these junctions with their atomically structures clarified, we still observe pronounced Josephson tunneling across the twisted boundary at different twist angles, in sharp contrast to the expectation from a pure d-wave pairing scenario. Also, we observe standard Fraunhofer patterns and integer Fiske steps—a manifestation of ac Josephson effect—in Bi-2201 junctions with twist angles close to 45 degrees. Together with the conventional temperature dependence of the Josephson current, our results strongly speak against d+id-wave pairing, which is recently proposed as an emergent property of twisted cuprate bicrystals. In general, the prominent Josephson tunneling in twisted Bi-2212 and Bi-2201 junctions favors the existence of a notable isotropic pairing component [4].

References:

[1] Y. Zhu, et al., Phys. Rev. X 11, 031011 (2021).

[2] Y. Zhu, et al., Phys. Rev. B 108, 174508 (2023).

[3] H. Wang, et al., Nat. Commun. 14, 5201 (2023).
[4] For a review in Chinese: D. Zhang, et al., Acta Phys. Sin. 72, 237402 (2023).

Biography

Ding Zhang is an associate professor at Department of Physics, Tsinghua University. He did his PhD study in Max Planck Institute for Solid State Research, Stuttgart, Germany from 2008 to 2014. He then joined Tsinghua University as a post-doc. Since 2016, Ding Zhang started the tenure-track in Tsinghua University and got tenured in 2022. He is an experimentalist in condensed matter physics, with the current interest in low-dimensional/high-temperature superconductivity, and low-temperature/high magnetic field transport techniques.

Division

Condensed Matter

Other information

Tencent Meeting link: https://meeting.tencent.com/dm/xWMhmX6kElSj

Meeting ID: 705 186 985, no password