The spatial variation of electronic states was imaged in the lightly doped Mott insulator Ca_{ 2-x}Na_{ x}CuO_{ 2}Cl_{ 2} using scanning tunneling microscopy / spectroscopy (STM/STS). We observed nano-scale domains with a high local density of states within an insulating background. The observed domains have a characteristic length scale of 2 nm (~4-5a, a:lattice constant) with preferred orientations along the tetragonal [100] direction. We argue that such spatially inhomogeneous electronic states are inherent to slightly doped Mott insulators and play an important role for the insulator to metal transition.
Categories: cond-mat.supr-con