  Design and synthesis of novel two-dimensional (2D) materials that possess
robust structural stability and unusual physical properties may open up
enormous opportunities for device and engineering applications. Herein we
propose a 2D sumanene lattice that be regarded as a derivative of the
conventional Kagome lattice. Our tight-binding analysis demonstrates sumanene
lattice contains two sets of Dirac cones and two sets of flat bands near the
Fermi surface, distinctively different from the Kagome lattice. Using
first-principles calculations, we theoretically suggest two possible routines
for realization of stable 2D sumanene monolayers (named as a phase and b
phase), and a-sumanene monolayer can be experimentally synthesized with
chemical vapor deposition using C21H12 as a precursor. Small binding energies
on Au(111) surface signify the possibility of their peel-off after grown on the
noble metal substrate. Importantly, our GW plus Bethe-Salpeter equation
calculations demonstrate both monolayers have moderate band gaps (1.94 eV for
a) and ultrahigh carrier mobilities (3.4*104 cm2/Vs for a). In particular,
a-sumanene monolayer possesses a strong exciton binding energy of 0.73 eV,
suggesting potential applications in optics.
