Dopant-induced nanoscale electronic inhomogeneities in Ca2-xSrxRuO4

Ca2-xSrxRuO4 single crystals with 0.1≤x≤2.0 have been studied systematically using scanning tunneling microscopy (STM) and spectroscopy, low-energy electron diffraction, and angle resolved photoelectron spectroscopy (ARPES). In contrast with the well-ordered lattice structure, the local density of states at the surface clearly shows a strong doping dependent nanoscale electronic inhomogeneity, regardless of the fact of isovalent substitution. Remarkably, the surface electronic roughness measured by STM and the inverse spectral weight of quasiparticle states determined by ARPES are found to vary with x in the same manner as the bulk in-plane residual resistivity, following the Nordheim rule. For the first time, the surface measurements-especially those with STM-are shown to be in good agreement with the bulk transport results, all clearly indicating a doping-induced electronic disorder in the system.