Theoretical studies on excitonic and half-metallic properties in 2D chalcogenides

In this talk, I will present theoretical investigation on two classes of chalcogenides with interesting properties, i.e., the saddle-point excitons and half-metallicity. First, monolayer b- and γ-phase group-IV monochalcogenides (MX, M = Ge or Sn; X = S or Se) are shown to possess saddle-point and camel’s back like band structure, respectively. While saddle-point exciton in b-MX leads to its strong adsorption, render them promising for solar cell applications with power conversion efficiencies as large as 1.11%,[1] a high-temperature exciton gas to electron-hole liquid transition can be achieved in γ-MX. Second, a class of CoGa₂X₄ (X= S, Se or Te) monolayer with triangular lattice exhibits intrinsic in-plane half-metallic ferromagnetism. The half-metal gaps are large enough (about 0.5 eV) to make them stable against the spin flip under weak external disturbances. We have systematically investigated the underlying origin of the ferromagnetism and predicted their high transition temperature T_C.[2]

Reference:
[1] N. Luo, et. al., Adv. Funct. Mater., 28, 1804581 (2018)
[2] S. Zhang, et. al., Adv. Funct. Mater., 29, 1808380 (2019)