Understanding the pairing mechanism of unconventional superconductors has been a central topic of condensed matter physics. To trace the pairing origin, we synthesized the first hole-doped chain cuprate thin film Ba_2-xSr­_xCuO_3+d and benchmarked the efficacy of the Hubbard model in these 1D cuprate chains by comparing angle-resolved photoemission spectroscopy (ARPES) experiments and exact theoretical solutions. We found that the Hubbard model is missing an important ingredient: An anomalously strong near-neighbor attractive term quantitatively explains experiments for all accessible dopings [1]. Interestingly, this ultra-strong near-neighbor attraction can be explained by long-range electron-phonon coupling using Hubbard-extended-Holstein model with real experimental parameters [2]. Moreover, by comparison of electronic structures between isostructural infinite layer cuprates and nickelates, we confirm an experimental correlation between higher T_C and stronger oxygen 2p hybridizations, which further hints the critical role of oxygen associated electron-phonon coupling for superconductivity [3]. Combining these findings, a holistic picture of cuprate superconducting pairing is emerging.

[1] Z. Chen, Y. Wang et al. Science 373, 1235 (2021).
[2] Y. Wang, Z. Chen et al. Phys. Rev. Lett. 127, 197003 (2021).
[3] Z. Chen et al. arXiv:2106.03963 (2021).

Dr. Zhuoyu Chen is currently a postdoc fellow in photon science at Stanford University, working with Prof. Zhi-Xun Shen. He obtained his B.S. in Mathematics and Physics from Tsinghua University (2012) and Ph.D. in Applied Physics from Stanford University (2016, advisor Prof. Harold Y. Hwang). In 2011, he visited The University of Tokyo and worked with Prof. Yoshihiro Iwasa. Dr. Chen is a condensed matter physics experimentalist with expertise spanning from thin film heterostructure synthesis with molecular beam epitaxy and pulsed laser deposition to stat-of-the-art characterization tools such as dilution refrigerator ultra-low temperature transport and synchrotron angle-resolved photoemission spectroscopy. His research interests include high-TC unconventional superconductors, strongly correlated electrons, and industrial applications of high-TC materials.

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