Strain-Induced Enhancement of the Electron Energy Relaxation in Strongly Correlated Superconductors

• Published in: Physical review. X 2014-03, Vol.4 (1), p.011056, Article 011056
• Main Authors: Gadermaier, C., Kabanov, V. V., Alexandrov, A. S., Stojchevska, L., Mertelj, T., Manzoni, C., Cerullo, G., Zhigadlo, N. D., Karpinski, J., Cai, Y. Q., Yao, X., Toda, Y., Oda, M., Sugai, S., Mihailovic, D.
• Format: Article
• Language: English
• Subjects: Coupling; Crossovers; Crystallography; Cuprates; Doping; Electron energy; Electron phonon interactions; Electronic materials; Group 5A compounds; High temperature superconductors; Lattice parameters; Phonons; Room temperature; Spectrum analysis; Superconductivity; Temperature
• ISSN: 2160-3308; 2160-3308
• DOI: 10.1103/PhysRevX.4.011056

We use femtosecond optical spectroscopy to systematically measure the primary energy relaxation rate Γ1 of photoexcited carriers in cuprate and pnictide superconductors. We find that Γ1 increases monotonically with increased negative strain in the crystallographic a axis. Generally, the Bardeen-Shockley deformation potential theorem and, specifically, pressure-induced Raman shifts reported in the literature suggest that increased negative strain enhances electron-phonon coupling, which implies that the observed direct correspondence between a and Γ1 is consistent with the canonical assignment of Γ1 to the electron-phonon interaction. The well-known nonmonotonic dependence of the superconducting critical temperature Tc on the a -axis strain is also reflected in a systematic dependence Tc on Γ1 , with a distinct maximum at intermediate values (∼16ps−1 at room temperature). The empirical nonmonotonic systematic variation of Tc with the strength of the electron-phonon interaction provides us with unique insight into the role of electron-phonon interaction in relation to the mechanism of high-Tc superconductivity as a crossover phenomenon.