Valley-selective directional emission from a transition-metal dichalcogenide monolayer mediated by a plasmonic nanoantenna.

Haitao Chen,Lei Xu,Mingkai Liu,Dragomir N Neshev

doi:10.3762/bjnano.9.71

Abstract

Background: Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) with intrinsically crystal inversion-symmetry breaking have shown many advanced optical properties. In particular, the valley polarization in 2D TMDCs that can be addressed optically has inspired new physical phenomena and great potential applications in valleytronics.Results: Here, we propose a TMDC–nanoantenna system that could effectively enhance and direct emission from the two valleys in TMDCs into diametrically opposite directions. By mimicking the emission from each valley of the monolayer of WSe2 as a chiral point-dipole emitter, we demonstrate numerically that the emission from different valleys is directed into opposite directions when coupling to a double-bar plasmonic nanoantenna. The directionality derives from the interference between the dipole and quadrupole modes excited in the two bars, respectively. Thus, we could tune the emission direction from the proposed TMDC–nanoantenna system by tuning the pumping without changing the antenna structure. Furthermore, we discuss the general principles and the opportunities to improve the average performance of the nanoantenna structure.Conclusion: The scheme we propose here can potentially serve as an important component for valley-based applications, such as non-volatile information storage and processing.

Highlights

The inversion-symmetry breaking and quantum confinement in monolayer transition-metal dichalcogenides (TMDCs) offer unprecedented opportunities to explore valley-based physics and applications [1,2,3]
Optical pumping of excitons of a specific valley polarization has been demonstrated by polarization-resolved photoluminescence (PL) measurements [12,13,14], where the chirality of the PL emission is the same as the pumping light, since different valleys are addressed by the angular momentum of the excitation
Based on the phase-locked excitation and interferences of these resonances, we have shown that the scattering direction of the TMDC–nanoantenna system is valley-locked

Summary

Introduction

The inversion-symmetry breaking and quantum confinement in monolayer TMDCs offer unprecedented opportunities to explore valley-based physics and applications [1,2,3]. Monolayer TMDCs with direct bandgap at the K and K′ points [11] make it possible to control the valley degree freedom entirely optically. Optical pumping of excitons of a specific valley polarization has been demonstrated by polarization-resolved photoluminescence (PL) measurements [12,13,14], where the chirality of the PL emission is the same as the pumping light, since different valleys are addressed by the angular momentum of the excitation. The valley polarization in 2D TMDCs that can be addressed optically has inspired new physical phenomena and great potential applications in valleytronics

Methods

Results

Conclusion