Electronic structure of monolayer Pb on SiC

Atomic monolayers with honeycomb structures are the ultimate limit of quantum spin Hall insulators (QSHI). The Kane-Mele model suggests that graphene is a QSHI. However, carbon is such a light element that its spin-orbit coupling (SOC) is weak and the resulting bulk gap is tiny. Therefore, 2D honeycomb structures consisting of heavy elements of group 14 such as Ge, Sn, and Pb gain a lot of attention because these elements introduce stronger SOC in the system. Although Pb is the most promising candidate for QSHI among group 14 elements, investigation of the 2D Pb system remains elusive. We investigated the electronic structure of monolayer Pb on SiC (0001) using angle-resolved photoemission spectroscopy (ARPES), scanning tunneling microscope (STM), and scanning transmission electron microscope (STEM). Our ARPES result has a reasonable agreement with the calculated band structure. In addition, our STM data show a stripe pattern of Pb atoms with a width of several nanometers, which might be induced by the geometric constraints of the SiC (0001) substrate. In this session, we will discuss our experimental and theoretical results.