Resonant Inelastic X-Ray Scattering Study of Electron-Exciton Coupling in High-T_{c} Cuprates

• Published in: Physical review. X 2022-06, Vol.12 (2), p.021068
• Main Authors: F. Barantani, M. K. Tran, I. Madan, I. Kapon, N. Bachar, T. C. Asmara, E. Paris, Y. Tseng, W. Zhang, Y. Hu, E. Giannini, G. Gu, T. P. Devereaux, C. Berthod, F. Carbone, T. Schmitt, D. van der Marel
• Format: Article
• Language: English
• ISSN: 2160-3308
• DOI: 10.1103/PhysRevX.12.021068

Explaining the mechanism of superconductivity in the high-T_{c} cuprates requires an understanding of what causes electrons to form Cooper pairs. Pairing can be mediated by phonons, the screened Coulomb force, spin or charge fluctuations, excitons, or by a combination of these. An excitonic pairing mechanism has been postulated, but experimental evidence for coupling between conduction electrons and excitons in the cuprates is sporadic. Here we use resonant inelastic x-ray scattering to monitor the temperature dependence of the [under d]_d exciton spectrum of Bi_{2}Sr_{2}CaCu_{2}O_{8-x} crystals with different charge carrier concentrations. We observe a significant change of the [under d]_d exciton spectra when the materials pass from the normal state into the superconductor state. Our observations show that the [under d]_d excitons start to shift up (down) in the overdoped (underdoped) sample when the material enters the superconducting phase. We attribute the superconductivity-induced effect and its sign reversal from underdoped to overdoped to the exchange coupling of the site of the [under d]_d exciton to the surrounding copper spins.