Since the discovery of high-temperature superconductivity in cuprates, Josephson junction based phase-sensitive experiments are believed and used to provide the most convincing evidence for determining the pairing symmetry. Regardless of different junction materials and geometries used, quantum tunneling involved in these experiments is essentially a nanoscale process, and thus, actual experimental results are extremely sensitive to atomic details of the junction structures. The situation has led to controversial results as to the nature of the pairing symmetry of cuprates: while in-plane junction expeJosephson junction based phase sensitive experiments provide the most convincing evidence for detecting the pairing symmetry of high-temperature cuprate superconductors. Since the tunneling are extremely sensitive to the interface of the junctions, controversial results have been obtained [1-3]. In this talk, I will introduce our work based on out-of-plane twisted Josephson junctions made of Bi2Sr2CaCu2O8+x (Bi-2212) which reveal significant s-wave component in paring symmetry [4]. We fabricated hundreds of atomically flat Josephson junctions at different twist angles with the vdW stacking technique. Josephson tunneling has been repeatedly observed in junctions with 45° twist angle, providing unambiguous evidence for presence of s-wave order parameter in the junctions.
Slides can be downloaded here (PDF format).
References:
[1] C. C. Tsuei and J. R. Kirtley, Pairing Symmetry in Cuprate Superconductors. Rev. Mod. Phys. 72, 969 (2000).
[2] Q. Li, et al. Bi2Sr2CaCu2O8+x Bicrystal c-Axis Twist Josephson Junctions: A New Phase-Sensitive Test of Order Parameter Symmetry. Phys. Rev. Lett. 83, 4160 (1999).
[3] S. Y. Zhao, et al. Emergent Interfacial Superconductivity between Twisted Cuprate Superconductors. arXiv:2108.13455, (2021).
[4] Presence of s-Wave Pairing in Josephson Junctions Made of Twisted Ultrathin Bi2Sr2CaCu2O8+x Flakes, Zhu et al., Phys. Rev. X 11, 031011 (2021)
Location: Stueckelberg, Ecole de Physique
Time: Friday 5 November, 12:00 for pizza, 12:30 start discussion
Note that this is the first Flat Club with pizza! If you want to come, register at our doodle, and write whether you want pizza or not. Please also register if you plan on coming but don’t want pizza.