Control of the Valley Polarization in Monolayer MoS2 by Plasmonic Chiral Structures
Chien-Ju Lee1*, Hung-Chih Li1, Li-Syuan Lu1, Han Yeh1, Wen-Hao Chang1
1Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
* Presenter:Chien-Ju Lee,
Monolayer transition metal dichalcogenides (TMDs), a group of direct-bandgap semiconductors with two degenerate but inequivalent valleys, are promising candidates for developing valleytronic applications. Control of valley polarization in TMDs has been demonstrated by using the helicity of light. However, it remains difficult to create valley polarization by lifting the valley degeneracy using magnetic field due to the small valley Zeeman splitting for typical monolayer TMDs. On the other hand, plasmonic chiral structures have been demonstrated being able to create strong chiral optical near-field contrast. An imbalance between the left- and right-circularly polarized components of the optical density of states can be created, which can in turn affect carrier decay dynamics of materials in the near-field of such structures. Here, we report on manipulating valley polarization in monolayer MoS2 by plasmonic chiral structures based on Archimedean spiral antennas. A series of spiral antennas with different resonance wavelengths were fabricated on single-crystalline Au flakes using focused ion beam. As the chiral structure is on resonance with the excitonic emission of MoS2, a net valley polarization and a high degree of circularly polarized photoluminescence were measured even at room temperature. Our results demonstrate a route for tailoring the valley-dependent dynamics of carriers in monolayer TMDs and the opportunity for developing valley-based optoelectronic applications.

Keywords: 2D materials, Plasmonics, Valleytronics