Electron-Boson Coupling Constant of Oxygen-Deficient Y0.7Ca0.3Ba2Cu3O7-delta Measured by Ultrafast Spectroscopy

Abstract

The ultrafast dynamics in an (001) oxygen-deficient Y0.7Ca0.3Ba2Cu3O7-delta thin film were measured by using the ultrafast spectroscopy. According to the model of time-dependent distributions of electrons in the case of electron-phonon relaxation, the electron-boson coupling constant lambda could be directly obtained from the relaxation time of the transient reflectivity change (Delta R/R). For the overdoped case with T (c)=61.3 K and the underdoped case with T (c)=65.5 K, the relaxation time of Delta R/R is around 4.32 ps and 3.66 ps, respectively, which correspond to lambda similar to 0.06. However, the lambda become larger (similar to 0.15) in the optimal doped region with T (c)=82.1 K while the relaxation time of Delta R/R shrinks to similar to 1.51 ps. These results indicate that the lambda is strongly hole-doping dependent, which may govern the T (c) of cuprate superconductors.