Recent years have seen increasing interest in a new class of materials called gapped chiral fermion systems.  Examples include gapped topological surface states, biased bilayer graphene, and monolayers of group-VI transition metal dichalcogenides such as MoS2. These materials exhibit markedly different electronic and optical properties compared to conventional semiconductors. In this talk, I will show that both the effective mass approximation and the electric dipole approximation, two essential ingredients in our understanding of semiconductor optics, break down in chiral fermion systems. Instead, the Berry curvature and winding number, are needed for a complete description of the electronic properties of excitons in these systems, including their energy spectrum and optical selection rule.  Some application of our theory will be discussed.<br/>

Electronic properties of excitons in gapped chiral fermion systems

2019 Spring National Meeting

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