Doping-Dependent Phase Diagram of Ca-Doped YBCO Observed by Femtosecond Spectroscopy

Abstract

The quasiparticle relaxation dynamics in a single (001) Ca-doped YBCO (Y(0.7)Ca(0.3)Ba(2)Cu(3)O(7-delta) ) superconducting thin film was probed by using the femtosecond time-resolved spectroscopy. The (001) Y(0.7)Ca(0.3)Ba(2)Cu(3)O(7-delta) thin film was prepared on a (100)STO substrate by pulsed laser deposition. Through controlling the oxygen pressure and the annealing temperature within quartz tube, the doping level (0.08 < p < 0.22) in the phase diagram could be widely tuned from the overdoped region to the underdoped region with varying the hole concentration (p) in a single sample. In the overdoped region, two different components (positive/negative) were obviously identified in the transient reflectivity curves (Delta R/R). The negative component in Delta R/R emerges at T < T (c) and quickly defeated by the development of the positive component. The dramatic change in the positive component of Delta R/R arises well below T (c). However, this anomaly change does not appear in the underdoped region. Only the positive Delta R/R was clearly observed at whole temperatures. These results indicate that the scenario of high-T (c) superconductivity in the overdoped region would be different from the underdoped region.