Superconducting Volume Fraction in the Overdoped Regime of La_2-x_Sr_x_CuO_4_: Implication for a Phase Separation from the Magnetic-Susceptibility Measurement

We have grown a single crystal of La 2- x Sr x CuO 4 in which the Sr concentration, x , continuously changes from 0.24 to 0.29 in the overdoped regime and obtained many pieces of single crystals with different x values by slicing the single crystal. From detailed measurements of the magnetic susceptibility, χ, of each piece, it has been found that the absolute value of χ at the measured lowest temperature 2 K, |χ 2 K |, on field cooling rapidly decreases with increasing x as well as the superconducting (SC) transition temperature. As the value of |χ 2 K | is regarded as corresponding to the SC volume fraction in a sample, it has been concluded that a phase separation into SC and normal-state regions occurs in a sample of La 2- x Sr x CuO 4 in the overdoped regime.