title: Tightly bound trions in monolayer MoS2.
abstract: Two-dimensional (2D) atomic crystals, such as graphene and transition-metal dichalcogenides, have emerged as a new class of materials with remarkable physical properties. In contrast to graphene, monolayer MoS(2) is a non-centrosymmetric material with a direct energy gap. Strong photoluminescence, a current on/off ratio exceeding 10(8) in field-effect transistors, and efficient valley and spin control by optical helicity have recently been demonstrated in this material. Here we report the spectroscopic identification in a monolayer MoS(2) field-effect transistor of tightly bound negative trions, a quasiparticle composed of two electrons and a hole. These quasiparticles, which can be optically created with valley and spin polarized holes, have no analogue in conventional semiconductors. They also possess a large binding energy (~ 20 meV), rendering them significant even at room temperature. Our results open up possibilities both for fundamental studies of many-body interactions and for optoelectronic and valleytronic applications in 2D atomic crystals.
authors.affiliation: Departments of Physics and Electrical Engineering, Columbia University, New York, NY 10027, USA.
authors.forename: Kin Fai
authors.initials: KF
authors.lastname: Mak
authors.forename: Keliang
authors.initials: K
authors.lastname: He
authors.forename: Changgu
authors.initials: C
authors.lastname: Lee
authors.forename: Gwan Hyoung
authors.initials: GH
authors.lastname: Lee
authors.forename: James
authors.initials: J
authors.lastname: Hone
authors.forename: Tony F
authors.initials: TF
authors.lastname: Heinz
authors.forename: Jie
authors.initials: J
authors.lastname: Shan