title: Population pulsation resonances of excitons in monolayer MoSe2 with sub-1  μeV linewidths.
abstract: Monolayer transition metal dichalcogenides, a new class of atomically thin semiconductors, possess optically coupled 2D valley excitons. The nature of exciton relaxation in these systems is currently poorly understood. Here, we investigate exciton relaxation in monolayer MoSe_{2} using polarization-resolved coherent nonlinear optical spectroscopy with high spectral resolution. We report strikingly narrow population pulsation resonances with two different characteristic linewidths of 1 and <0.2  μeV at low temperature. These linewidths are more than 3 orders of magnitude narrower than the photoluminescence and absorption linewidth, and indicate that a component of the exciton relaxation dynamics occurs on time scales longer than 1 ns. The ultranarrow resonance (<0.2  μeV) emerges with increasing excitation intensity, and implies the existence of a long-lived state whose lifetime exceeds 6 ns.
authors.affiliation: Department of Physics, University of Washington, Seattle, Washington 98195, USA.
authors.forename: John R
authors.initials: JR
authors.lastname: Schaibley
authors.affiliation: Department of Physics, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Todd
authors.initials: T
authors.lastname: Karin
authors.affiliation: Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China.
authors.forename: Hongyi
authors.initials: H
authors.lastname: Yu
authors.affiliation: Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Jason S
authors.initials: JS
authors.lastname: Ross
authors.affiliation: Department of Physics, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Pasqual
authors.initials: P
authors.lastname: Rivera
authors.affiliation: Department of Physics, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Jones
authors.affiliation: Department of Physics, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Marie E
authors.initials: ME
authors.lastname: Scott
authors.affiliation: Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.|Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.
authors.forename: Jiaqiang
authors.initials: J
authors.lastname: Yan
authors.affiliation: Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.|Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.|Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA.
authors.forename: D G
authors.initials: DG
authors.lastname: Mandrus
authors.affiliation: Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China.
authors.forename: Wang
authors.initials: W
authors.lastname: Yao
authors.affiliation: Department of Physics, University of Washington, Seattle, Washington 98195, USA.|Department of Electrical Engineering, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Kai-Mei
authors.initials: KM
authors.lastname: Fu
authors.affiliation: Department of Physics, University of Washington, Seattle, Washington 98195, USA.|Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Xu