T linearity of in-plane resistivity in Bi ₂Sr ₂CaCu ₂O _8+δ thin films

We performed a temperature and doping-dependent study of in-plane dc resistivity (IDCR) on molecular beam epitaxy grown Bi ₂Sr ₂CaCu ₂O _8+δ thin films. By analyzing the temperature dependence of normal state IDCR as a function of doping level, we show that long-known T-linear dependence of normal state IDCR occurs not at the optimal doping (p=0.16/Cu) but at an overdoping of p=0.19/Cu, which coincides with the recently proposed putative quantum critical point. This observation suggests that p=0.19 may be a sample-independent critical doping level at least for bilayer cuprate systems.