Anisotropic Resistivities of Precisely Oxygen Controlled Single-Crystal Bi2Sr2CaCu2O8+δ: Systematic Study on “Spin Gap” Effect

摘要: The in-plane resistivity ${\ensuremath{\rho}}_{a}(T)$ and the out-of-plane ${\ensuremath{\rho}}_{c}(T)$ have been systematically measured for ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ single crystals with their oxygen contents precisely controlled. In underdoped region, deviation from $T$-linear resistivity, which evidences opening of ``spin gap,'' is clearly observed, while well reproduced by activation-type phenomenological formula ${\ensuremath{\rho}}_{c}(T)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(a/T)\mathrm{exp}(\ensuremath{\Delta}/T)+c$. contrast to ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ system, we find that onset semiconducting does not coincide spin gap seen in this system.