STM/STS study on Ca2-xNaxCuO2Cl2 single crystals

To explore the evolution of electronic states from the Mott insulator to the high-Tc superconductor, we performed scanning tunneling microscopy/spectroscopy on Ca2-xNaxCuO2Cl2 single crystals which show superior cleavage. Topographic images taken by constant-current scanning at 7 K show clear atomic images superposed on nano-scale patch-like or river-like irregular corrugations. Spectroscopic measurements revealed that low areas are semiconducting and the spectrum at high area is approaching to 'metallic' while gap-like feature still remains near the Fermi level. Namely, background corrugations are originated from the electronic inhomogeneity