Doping phase diagram of Y_(1-x)Ca_xBa_2(Cu_(1-y)Zn_y)_3O_(7-δ) from transport measurements: Tracking the pseudogap below T_c

摘要

The effects of planar hole concentration, p, and magnetic field on the resistivity, p(T), of high-quality c-axis oriented crystalline thin films and sintered Y_(1-x)Ca_xBa_2(Cu_(1-y)Zn_y)_3O_(7-δ) samples were investigated over a wide range of Ca, Zn, and oxygen contents. Zn was used to suppress superconductivity and this enabled us to extract the characteristic pseudogap temperature, T~*(p) below T_(c0)(p[≡T_c(x=0, y=0)]. We have also located the characteristic temperature, T_(scf) marking the onset of significant superconducting fluctuations above T_c, from the analysis of p(T,H,p) and p(T,p) data. From this we are able to identify T~*(p) near the optimum doping level where the Values of T~* (p) and T_(scf) (p)are very close and hard to distinguish. We again found that T~* (p) depends only on the hole concentration p, and not on the level of disorder associated with Zn or Ca substitutions. We conclude that (ⅰ) T~* (p) (and therefore, the pseudogap) persists below T_(c0)(p) on the overdoped side and does not merge with the T_(c0)(p) line and (ⅱ) T`* (p) and the pseudogap energy extrapolate to zero at the doping p=0.19+-0.01.