The ratio of small polarons to free carriers in La2-xSrxCuO4 derived from susceptibility measurements

The normal-state spin susceptibility chi of La2-xSrxCuO4 was measured as a function of doping x. For x less than or equal to x(1) = 0.09, chi is well described by small-polaron theory. For x greater than or equal to x(1), a temperature-independent Pauli component is present in chi as well. These results indicate the coexistence of small polarons and free carriers above the transition concentration x(1). The concentration of the Free carriers increases rapidly with x-x(1), reaching a maximum for optimal doping (x = 0.15). The large mass anisotropy of the polarons is obtained quantitatively from the chi-measurements.