报告题目：Superconducting Surface Materials and Future Challenges

报 告 人：Dr. Takashi Uchihashi，International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Japan

报告时间：9月5日（周四） 下午3:00-4:00

报告地点：物理系三楼报告厅

报告摘要：Surface reconstructions of silicon and related semiconductors with metal adatoms constitute a family of highly-ordered low dimensional materials, which are fundamentally different from their bulk counterparts. They are of particular interest from the viewpoint of materials science because they will enable us to create and manipulate nanomaterials with an atomic precision. In addition, the intrinsic space-inversion symmetry breaking due to the presence of surface leads to the Rashba effects, thus adding spin-related elements to them [1].

In this talk, by performing direct and macroscopic electron transport measurements, I will demonstrate that the Si(111)-(？7×？3)-In surface becomes superconducting around 2.8K [2,3]. The superconducting transition is evidenced by observations of the zero resistance state and of I − V characteristics exhibiting sharp and hysteretic switching below 2.8 K ( ？ Tc). This macroscopic supercurrent also shows a significant robustness; the two-dimensional (2D) critical current density J_2D,cis estimated to be as high as 1.8 A/m at 1.8 K. Furthermore, the observed temperature dependence of critical current density J_2D,cindicates that the surface atomic steps serve as strongly coupled Josephson junctions. Typical 2D characteristics such as the Cooper pair fluctuation effect and vortex-driven electron dissipation are found for this system [4].

I also describe our attempt to control the superconducting properties of the Si(111)-(？7×？3)-In surface by organic molecular layers. Co-phthalocyanine (Pc) molecules were found to be grown epitaxially on the Si(111)-(？7×？3)-In surface. Even after the molecular growth, the sample was found to exhibit a clear superconducting transition. This promises the use of molecules to control the properties of surface superconductors. One of its important applications will be fabrication of topological superconductors based on a hybrid layered structure.

References

[1] K. Yaji et al., Nat. Commun. 1, 17 (2010).

[2] T. Zhang et al., Nature Phys. 6, 104 (2010).

[3] T. Uchihashi et al., Phys. Rev. Lett. 107, 207001 (2011).

[4] T. Uchihashi et al., Nanoscale Res. Lett. 8, 167 (2013) .