Symmetry-dependent electronic Raman scattering inLa2−xSrxCuO4: Evidence for doping-induced change in thek-space anisotropy of charge dynamics

Low-frequency electronic Raman scattering in ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$ has been investigated over a wide compositional region, 0≤x≤0.34, covering the insulating, superconducting, and nonsuperconducting metallic compounds. We have found that the scattering intensity for the (xy) polarization predominates over that of the (x’y’) polarization in the low-doping region below x≤0.15, but vice versa at higher doping levels. The results indicate that anisotropy in the effective-mass tensor (or k-space dispersion) of the carriers changes systematically with hole doping, in contradiction with the simple band picture.