title: Nonanalyticity, Valley Quantum Phases, and Lightlike Exciton Dispersion in Monolayer Transition Metal Dichalcogenides: Theory and First-Principles Calculations.
abstract: Exciton dispersion as a function of center-of-mass momentum Q is essential to the understanding of exciton dynamics. We use the ab initio GW-Bethe-Salpeter equation method to calculate the dispersion of excitons in monolayer MoS(2) and find a nonanalytic lightlike dispersion. This behavior arises from an unusual |Q|-term in both the intra- and intervalley exchange of the electron-hole interaction, which concurrently gives rise to a valley quantum phase of winding number two. A simple effective Hamiltonian to Q(2) order with analytic solutions is derived to describe quantitatively these behaviors.
authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA.|Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Diana Y
authors.initials: DY
authors.lastname: Qiu
authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA.|Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Ting
authors.initials: T
authors.lastname: Cao
authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA.|Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Steven G
authors.initials: SG
authors.lastname: Louie