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

• Published in: arXiv.org 2022-06
• Main Authors: Barantani, F, Tran, M K, Madan, I, Kapon, I, Bachar, N, Asmara, A 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: Article
• Language: English
• Subjects: Bismuth strontium calcium copper oxide; Carrier density; Conduction electrons; Cooper pairs; Coupling; Cuprates; Current carriers; Electrons; Excitation spectra; Excitons; Inelastic scattering; Superconductivity; Temperature dependence; X-ray scattering
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2108.06118

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 (RIXS) to monitor the temperature dependence of the \(\underline{d}d\) exciton spectrum of Bi\(_2\)Sr\(_2\)CaCu\(_2\)O\(_{8-x}\) (Bi-2212) crystals with different charge carrier concentrations. We observe a significant change of the \(\underline{d}d\) exciton spectra when the materials pass from the normal state into the superconductor state. Our observations show that the \(\underline{d}d\) 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 \(\underline{d}d\) exciton to the surrounding copper spins.