The electronic ground state in high-$T_{ \rm c}$ cuprates where the superconducting state is suppressed by Ni substitution has been investigated in La$_{ 2-x}$Sr$_x$Cu$_{ 1-y}$Ni$_y$O$_4$ from the specific heat and muon spin relaxation measurements. It has been found that the ground state changes from a magnetically ordered state with the strong hole-trapping by Ni to a metallic state with the Kondo effect of Ni with increasing hole-concentration. Moreover, the analysis of the results has revealed that a phase separation into the magnetically ordered phase and the metallic phase occurs around the boundary of two phases.
Categories: cond-mat.supr-con cond-mat.str-el