Nanoscale Optical Addressing of Valley Pseudospins through Transverse Optical Spin

Abstract

Valley pseudospin has emerged as a good quantum number to encode information, analogous to spin in spintronics. Two-dimensional transition metal dichalcogenides (2D TMDCs) recently attracted enormous attention for their easy access to the valley pseudospin through valley-dependent optical transitions. Different ways have been reported to read out the valley pseudospin state. For practical applications, on-chip access to and manipulation of valley pseudospins is paramount, not only to read out but especially to initiate the valley pseudospin state. Here, we experimentally demonstrate the selective on-chip, optical near-field initiation of valley pseudospins at room temperature. We exploit a nanowire optical waveguide, such that the local transverse optical spin of its guided modes selectively excites a specific valley pseudospin. Furthermore, spin-momentum locking of the transverse optical spin enables us to flip valley pseudospins with the opposite propagation direction. Thus, we open up ways to realize integrated hybrid opto-valleytronic devices.

Plasmonic Modulation of Valleytronic Emission in Two‐Dimensional Transition Metal Dichalcogenides

“…c,d) Reproduced with permission. [ 76 ] Copyright 2020, American Chemical Society. e) Schematic and scanning electron microscope image (SEM) of asymmetric grooves.…”

“…Very recently, in another work, ZnO nanowire as a waveguide excites valley pseudospins selectively in a few‐layer WS 2 and flips valley pseudospins with the opposite waveguide propagation direction by focusing the linearly polarized laser at one of the selected nanowire ends, as shown in Figure 2c. [ 76 ] The emitted light is collected on the glass substrate side in the far‐field. As a reverse process of the former study, the unidirectional propagated waveguide can excite opposite valley polarizations on two sides of the nanowire and induce opposite circularly polarized PL by SPP due to the spin‐momentum locking.…”

Group Velocity Modulation and Light Field Focusing of the Edge States in Chirped Valley Graphene Plasmonic Metamaterials

“…Valley degrees of freedom (DOF), also known as valley pseudospins, mark discrete extreme energy states in the momentum space [ 1 , 2 , 3 , 4 , 5 ]. Valley pseudospin appears widely not only in conventional semiconductor materials, but also in classical wave artificial crystals, such as phononic crystals [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ] and photonic crystals (PhCs) [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. Similar to the spin DOF in spintronics, the valley DOF is regarded as a new information carrier [ 18 , 23 , 24 ] and provides a more effective method of dealing with the nontrivial topological phase [ 21 , 22 , 23 , 24 , 25 ] which makes valley topological photonics become a research field in the current frontier.…”

Morphology-induced spectral modification of self-assembled WS2 pyramids

“…A pseudospin can be attributed to each of the two valleys 2D TMDs possess, making it possible to address them selectively with circularly polarized light. [2][3][4] The electronic and optical properties of these 2D semiconductors, for instance the excitons and valley pseudospin, make them an interesting platform for opto-electronics 5,6 and valleytronics [7][8][9] applications.…”

“…One of the ways of creating 2D TMD monolayer samples is by exfoliation from bulk. 9 An alternative method to produce layered TMDs materials is Chemical Vapor Deposition (CVD). [10][11][12][13][14][15] While CVD can reproduce horizontal layers as found in naturally occurring TMDs, adjusting the growth conditions enables the growth of nanostructures with exciting properties and applications in nanotechnology, for instance vertical walls, owers and pyramids.…”