To elucidate a quantum phase transition (QPT) in Bi_2Sr_{ 2-x}La_xCuO_{ 6+\delta}, we measure charge and heat transport properties at very low temperatures and examine the following characteristics for a wide range of doping: normal-state resistivity anisotropy under 58 T, temperature dependence of the in-plane thermal conductivity K_{ ab}, and the magnetic-field dependence of K_{ ab}. It turns out that all of them show signatures of a QPT at the 1/8 hole doping. Together with the recent normal-state Hall measurements under 58 T that signified the existence of a QPT at optimum doping, the present results indicate that there are two QPTs in the superconducting doping regime of this material.
Categories: cond-mat.supr-con cond-mat.str-el