title: Trion-induced negative photoconductivity in monolayer MoS2.
abstract: Optical excitation typically enhances electrical conduction and low-frequency radiation absorption in semiconductors. We, however, observe a pronounced transient decrease of conductivity in doped monolayer molybdenum disulfide (MoS(2)), a two-dimensional (2D) semiconductor, using ultrafast optical-pump terahertz-probe spectroscopy. In particular, the conductivity is reduced to only 30% of its equilibrium value at high pump fluence. This anomalous phenomenon arises from the strong many-body interactions in the 2D system, where photoexcited electron-hole pairs join the doping-induced charges to form trions, bound states of two electrons and one hole. The resultant increase of the carrier effective mass substantially diminishes the conductivity.
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: C H
authors.initials: CH
authors.lastname: Lui
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA and Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: A J
authors.initials: AJ
authors.lastname: Frenzel
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: D V
authors.initials: DV
authors.lastname: Pilon
authors.affiliation: Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA and Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan.
authors.forename: Y-H
authors.initials: YH
authors.lastname: Lee
authors.affiliation: Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: X
authors.initials: X
authors.lastname: Ling
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: G M
authors.initials: GM
authors.lastname: Akselrod
authors.affiliation: Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: J
authors.initials: J
authors.lastname: Kong
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: N
authors.initials: N
authors.lastname: Gedik