Abstract
Scanning tunneling microscopes (STM) that can operate under UHV at low temperatures have been developed. STM observations of Bi-based oxide superconductors have shown that Pb atoms occupying Bi sites and Sr-site defects could be imaged selectively by appropriately setting bias voltage. Furthermore, scanning tunneling spectroscopic measurements have successfully visualized electronic phase separation into superconducting and non-superconducting domains. A variable temperature SPM instrument with sub-micron scale resolution and wide scanning range up to 15mm has also been constructed. The instrument enables us to measure local magnetic and electric properties by using a miniature SQUID sensor and cylindrical resonator tube, respectively, as scanning probes. The former was applied to direct observation of vortices trapped in La1-xSrxCuO4. The latter was utilized to investigate conductivity of a Mn-based oxide, Nd1-xSrxMnO3, as functions of chemical composition x and temperature, in a systematic manner.
