Fluctuation conductivity analysis for Bi2Sr2(Ca1−xYx)Cu2O8+δ single crystals in both overdoped and underdoped regimes

In-plane fluctuation conductivity σab′ is studied in Bi2Sr2(Ca1−xYx)Cu2O8+δ single crystals with the doping level x   from the overdoped to underdoped regime. For the σab′ analysis, the Lawrence–Doniach (LD) theory is employed by taking account of a total-energy cutoff in the fluctuation spectrum, and a remarkable agreement is attained between theory and experiment over the whole temperature range investigated. From the theoretical fittings, it is found that not only the LD anisotropic parameter but also the cutoff parameter show specimen-dependent natures. The behavior of these parameters upon doping allows us to conclude that starting from the optimal doping level, the anisotropy of our Bi2212 system is highly enhanced in the underdoped region while also enhanced moderately as the system enters into the overdoped region. The present results are discussed in comparison to other studies of fluctuation effects in related systems.