Hole concentration and phonon renormalization of the 340-cm-1 B1g mode in 2% Ca-doped YBa2Cu3Oy (6.76≤y≤7.00) -: art. no. 064514

In order to access the overdoped regime of the YBa2Cu3Oy phase diagram, 2% Ca is substituted for Y in YBa2Cu3Oy (y=7.00,6.93,6.88,6.76). Raman scattering studies have been carried out on these four single crystals. Measurements of the superconductivity-induced renormalization in frequency (Deltaomega) and linewidth (Delta2gamma) of the 340-cm(-1) B-1g phonon demonstrate that the magnitude of the renormalization is directly related to the hole concentration p and not simply the oxygen content. The changes in Deltaomega with p imply that the superconducting gap (Delta(max)) decreases monotonically with increasing hole concentration in the overdoped regime, and Deltaomega falls to zero in the underdoped regime. The linewidth renormalization Delta2gamma is negative in the underdoped regime, crossing over at optimal doping to a positive value in the overdoped state.