[1Ca02-12] SS1

[1Ca08] Role of steps on superconductor-insulator transition in mono-atomic-layer metal films grown on semiconducting substrates

*Yudai Sato¹, Masahiro Haze¹, Shunsuke Yoshizawa², Takashi Uchihashi², Yukio Hasegwa¹ (1. The Institute for Solid State Physics, The University of Tokyo, 2. National Institute for Materials Science)

We characterized the magnetic-field-driven superconductor-insulator transition (SIT) of Pb mono-atomic-layer thin films formed on Si(111) substrates with various step density by electrical conductance measurements and scanning tunneling microscopy / spectroscopy (STM/S). From the conductance measurements, we found that the critical temperature is lowered but the orbital critical magnetic field is enhanced with the step density. In addition, the behavior of the anomalous metallic state, which is often observed on highly crystalline 2D superconductors, depends on the step density. Interestingly, in the case of the sample with large step density, the superconducting gap still remains under magnetic fields above the orbital critical field. We expect that the remaining gap implies the presence of Bose insulating phase, in which the Cooper pairs are still remaining but localized.