Two-dimensional semiconductors such as monolayer transition metal dichalcogenides (TMDs) exhibits remarkable optical properties such as robust valley polarization, making them ideal for optoelectronic and valleytronic devices. Manipulating the valley polarization by optical method is the key to realize valleytronic devices. Here, we demonstrate a resonant plasmonic nanostructure designed to spatially separate the emissions from different valleys of the WSe2 monolayer at cryogenic temperature. By changing the helicity of excitation, we show the directionality control of valley-based emission. Our hybrid nanostructure exhibits the possibility to realise the valleytronic devices.
Two-dimensional transition metal dichalcogenides (TMDCs) show a great potential for optoelectronic applications due to their unique properties. However, the control of their emission through coupling to nanoantennas remains largely unexplored. Importantly, antenna-TMDCs coupling promised to be an effective way for PL control due to the high Purcell enhancement such plasmonic nanostructures can offer. MoSe2, a member of the TMDCs family, is an appealing candidate for coupling to gold plasmonic nanostructures due to its smaller bandgap and higher electron mobility in comparison to the readily used MoS2. Moreover, the PL of MoSe2 occurs in the near-infrared spectral range, where the emissive properties do not suffer from the enhanced dissipation in the gold due to interband transitions.
Here we study the interaction between monolayer MoSe2 and plasmonic dipolar antennas demonstrating efficient control of the PL from the TMDC layer. In our experiments, we transfer an exfoliated monolayer MoSe2 onto an array of rectangular gold nanoantenna whose plasmonic resonances overlap with the PL emission of the material. By varying a thickness of the spacer between the MoSe2 layer and the nanoantenna, we demonstrate tuneable PL from threefold enhancement (sample with spacer) to twice quenching (sample without spacer). Furthermore, the observed PL from the TMDC-antenna system demonstrates polarization-dependent properties, thus offering the possibility of polarization-based PL control. Our experimental results are supported by numerical simulations. To the best of our knowledge, this is the first study of Au-MoSe2 plasmonic hybrid structures realizing flexible PL manipulation, which is promising for future optoelectronic applications.
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