Title: From a normal insulator to a topological insulator in plumbene,
Abstract: Plumbene, similar to silicene, has a buckled honeycomb structure with a large
band gap ($\sim 400$ meV). All previous studies have shown that it is a normal
insulator. Here, we perform first-principles calculations and employ a
sixteen-band tight-binding model with nearest-neighbor and
next-nearest-neighbor hopping terms to investigate electronic structures and
topological properties of the plumbene monolayer. We find that it can become a
topological insulator with a large bulk gap ($\sim 200$ meV) through electron
doping, and the nontrivial state is very robust with respect to external
strain. Plumbene can be an ideal candidate for realizing the quantum spin Hall
effect at room temperature. By investigating effects of external electric and
magnetic fields on electronic structures and transport properties of plumbene,
we present two rich phase diagrams with and without electron doping, and
propose a theoretical design for a four-state spin-valley filter.