Rapid change of superconductivity and electron-phonon coupling through critical doping in Bi-2212.

He, Y; Hashimoto, M; Song, D; Chen, S-D; He, J; Vishik, I M; Moritz, B; Lee, D-H et al. · Science · 2018

basic_science · Level V

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Abstract

Electron-boson coupling plays a key role in superconductivity for many systems. However, in copper-based high-critical temperature (<i>T</i> <sub>c</sub>) superconductors, its relation to superconductivity remains controversial despite strong spectroscopic fingerprints. In this study, we used angle-resolved photoemission spectroscopy to find a pronounced correlation between the superconducting gap and the bosonic coupling strength near the Brillouin zone boundary in Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>8+δ</sub> The bosonic coupling strength rapidly increases from the overdoped Fermi liquid regime to the optimally doped strange metal, concomitant with the quadrupled superconducting gap and the doubled gap-to-<i>T</i> <sub>c</sub> ratio across the pseudogap boundary. This synchronized lattice and electronic response suggests that the effects of electronic interaction and the electron-phonon coupling (EPC) reinforce each other in a positive-feedback loop upon entering the strange-metal regime, which in turn drives a stronger superconductivity.