Valley-Selective Response of Nanostructures Coupled to 2D Transition-Metal Dichalcogenides

Alexander Krasnok,Andrea Alù

doi:10.3390/app8071157

Abstract

Monolayer (1L) transition-metal dichalcogenides (TMDCs) are attractive materials for several optoelectronic applications because of their strong excitonic resonances and valley-selective response. Valley excitons in 1L-TMDCs are formed at opposite points of the Brillouin zone boundary, giving rise to a valley degree of freedom that can be treated as a pseudospin, and may be used as a platform for information transport and processing. However, short valley depolarization times and relatively short exciton lifetimes at room temperature prevent using valley pseudospins in on-chip integrated valley devices. Recently, it was demonstrated how coupling these materials to optical nanoantennas and metasurfaces can overcome this obstacle. Here, we review the state-of-the-art advances in valley-selective directional emission and exciton sorting in 1L-TMDC mediated by nanostructures and nanoantennas. We briefly discuss the optical properties of 1L-TMDCs paying special attention to their photoluminescence/absorption spectra, dynamics of valley depolarization, and the valley Hall effect. Then, we review recent works on nanostructures for valley-selective directional emission from 1L-TMDCs.

Highlights

As the growth of electronics and computing infrastructure nears the limits of the so-called Moore’s law [1], new directions in information processing and harvesting become of crucial importance in today’s technology
The paper is organized as follows: in Section 2, we briefly discuss the optical properties of two-dimensional (2D) transition-metal dichalcogenides (TMDCs) materials, paying special attention to their photoluminescence/absorption spectra, dynamics of valley depolarization, and the valley Hall effect; in Section 3, we summarize recent published work devoted to nanostructures for 1L-TMDC valley separation
As mentioned in the introduction, the proposed nanostructures for valley-selective response can perform spatial separation of the valley degree of freedom with surface waves or separation in K-space when photons with opposite helicity are emitted in different directions

Summary

Introduction

As the growth of electronics and computing infrastructure nears the limits of the so-called Moore’s law [1], new directions in information processing and harvesting become of crucial importance in today’s technology. At it was prevent short valley depolarization and relatively room demonstrated how coupling these materials to optical nanoantennas and metasurfaces can temperature prevent using valley pseudospin in on-chip integrated valley devices. Degree-of-freedom separation (valley-selective directional emission and exciton sorting) mediated paper isand devoted to reviewing in 1L-TMDC valley byThis nanostructures nanoantennas. 2, we briefly degree-of-freedom separation (valley-selective directional emission and exciton sorting) mediated discuss the optical properties of two-dimensional (2D) TMDC materials, paying special attention to by nanostructures and nanoantennas. The paper is organized as follows: in Section 2, we briefly discuss the optical properties of two-dimensional (2D) TMDC materials, paying special attention to their photoluminescence/absorption spectra, dynamics of valley depolarization, and the valley Hall effect; in Section 3, we summarize recent published work devoted to nanostructures for 1L-TMDC valley separation. Special attention is devoted to our and our collaborators’ recent results in this area

Optical Properties of 1L-TMDCs

Single Nanoantennas

Conclusions