Resonant Inelastic X-Ray Scattering Study of Electron-Exciton Coupling in High-Tc Cuprates

• Published in: Physical review. X Vol. 12; no. 2
• Main Authors: Barantani, F, Tran, M K, Madan, I, Kapon, I, Bachar, N, Asmara, T C, Paris, E, Tseng, Y, Zhang, W, Y. Hu, Giannini, E, G. Gu, Devereaux, T P, Berthod, C, Carbone, F, Schmitt, T, van der Marel, D
• Format: Journal Article
• Language: English
• Published: College Park American Physical Society 29-06-2022; American Physical Society (APS)
• Subjects: Carrier density; Colossal magnetoresistance; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Conduction electrons; Cooper pairs; Copper oxides; Coupling; Cuprates; Current carriers; Excitons; High temperature superconductors; Inelastic scattering; Magnetoresistivity; pairing mechanisms; Phonons; resonant inelastic x-ray scattering; Superconductivity; Temperature dependence; X-ray scattering
• ISSN: 2160-3308; 2160-3308
• DOI: 10.1103/PhysRevX.12.021068

Explaining the mechanism of superconductivity in the high-Tccuprates 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 thed_dexciton spectrum ofBi2Sr2CaCu2O8−xcrystals with different charge carrier concentrations. We observe a significant change of thed_dexciton spectra when the materials pass from the normal state into the superconductor state. Our observations show that thed_dexcitons 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 thed_dexciton to the surrounding copper spins.