title: Electrical control of second-harmonic generation in a WSe2 monolayer transistor.
abstract: Nonlinear optical frequency conversion, in which optical fields interact with a nonlinear medium to produce new field frequencies, is ubiquitous in modern photonic systems. However, the nonlinear electric susceptibilities that give rise to such phenomena are often challenging to tune in a given material and, so far, dynamical control of optical nonlinearities remains confined to research laboratories as a spectroscopic tool. Here, we report a mechanism to electrically control second-order optical nonlinearities in monolayer WSe₂, an atomically thin semiconductor. We show that the intensity of second-harmonic generation at the A-exciton resonance is tunable by over an order of magnitude at low temperature and nearly a factor of four at room temperature through electrostatic doping in a field-effect transistor. Such tunability arises from the strong exciton charging effects in monolayer semiconductors, which allow for exceptional control over the oscillator strengths at the exciton and trion resonances. The exciton-enhanced second-harmonic generation is counter-circularly polarized to the excitation laser due to the combination of the two-photon and one-photon valley selection rules, which have opposite helicity in the monolayer. Our study paves the way towards a new platform for chip-scale, electrically tunable nonlinear optical devices based on two-dimensional semiconductors.
authors.affiliation: Department of Physics, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Kyle L
authors.initials: KL
authors.lastname: Seyler
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 and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China.
authors.forename: Pu
authors.initials: P
authors.lastname: Gong
authors.affiliation: Department of Physics, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Pasqual
authors.identifier: 0000000259091686
authors.initials: P
authors.lastname: Rivera
authors.affiliation: Department of Physics, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Aaron M
authors.identifier: 0000000283261294
authors.initials: AM
authors.lastname: Jones
authors.affiliation: Department of Physics, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Sanfeng
authors.initials: S
authors.lastname: Wu
authors.affiliation: 1] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA [2] Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.
authors.forename: Jiaqiang
authors.initials: J
authors.lastname: Yan
authors.affiliation: 1] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA [2] Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA [3] Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA.
authors.forename: David 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.identifier: 0000000328834528
authors.initials: W
authors.lastname: Yao
authors.affiliation: 1] Department of Physics, University of Washington, Seattle, Washington 98195, USA [2] Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Xiaodong
authors.identifier: 0000000303482095
authors.initials: X
authors.lastname: Xu