Figure: STP results for phase. (upper) theTopographic image (middle) Electrochemical potential image (bottom) Line profiles showing the distribution of potential over terraces and steps.Fig. 1 STM topography of Sr/Na doped PbTe69Poster Award NomineePoster Award NomineeP3-13Measuring Electronic Structure of Thermoelectric Materials by Scanning Tunneling MicroscopyYuya Hattori1, Shunsuke Yoshizawa1, Keisuke Sagisaka1, Yuki Tokumoto2, Keiichi Edagawa2, Takako Konoike3, Shinya Uji3, and Taichi Terashima31 Center for Basic Research on Materials, National Institute for Materials Science (NIMS)2 Institute of Industrial Science, The University of Tokyo3 Research center for Materials Nanoarchitectonics, National Institute for Materials Science (NIMS)The dimensionless figure of merit (zT) of thermoelectric (TE) materials has been increasing rapidly in recent years. In the 1990s, the zT values of bulk thermoelectric materials are around zT~1.0, but high performance materials with zT>2.5 with doubled conversion efficiency are reported in many classes after 2010s. The drastic leap in performance stems from the band engineering. By adding dopants, it is possible to control the bandgap and to change the energy of the band edge, which is crucial for the TE performance. However, there was no experimental verification of the modification of the band structure by doping. Here, we use scanning tunneling microscopy (STM) to verify the band modification of Sr/Na doped PbTe [1], which is reported to have zT=2.5. By measuring the dI/dV values, which are proportional to the local density of states, we show that the band gap of Sr/Na doped PbTe becomes larger (350 meV) than the pristine PbTe (200 meV). We also find other band modifications, and the details will be discussed in the poster presentation.[1] Y. Hattori et al., Phys. Rev. B, 108, 125119 (2023).P3-14Structures and Surface Conductivity on Dense Pb Monolayers Formed on Si(111) Studied by Low Temperature Scanning Tunneling Microscopy/PotentiometryJunya Okazaki1, Masahiro Haze1, Masayuki Hamada1, Yudai Sato2, and Yukio Hasegawa11 The Institute for Solid State Physics, The University of Tokyo, Japan2 Leiden Institute of Physics, Leiden University, the NetherlandsIn two-dimensional superconductors, superconducting properties are sensitive to the presence of disorder. In the case of monolayer superconductors, atomic steps on the substrate are known to behave as disorders [1]. Because the manner in which the steps disturb the superconductivity depends on the monolayer structure, we investigated the resistivity of the atomic steps of various monolayers using low-temperature scanning tunneling microscopy/potentiometry (LT-STM/P). This method allows us to obtain surface images with atomic-scale spatial resolution and electrochemical potential images with μV resolution, providing information about the local surface transport properties. In this study, LT-STM/P measurements were performed on dense Pb atomic layers formed on Si(111) and revealed that the atomic step in the 1.2 monolayer (ML)- phase works as a stronger disorder than that in the 1.33 ML-striped incommensurate (SIC) phase. In this presentation, we discuss the differences in the surface electrical resistance between the two phases.[1] Y. Sato et al., PRL, 130, 106002 (2023).
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