Strain engineering is a natural route to control the electronic and optical properties of two-dimensional (2D) materials. Recently, 2D semiconductors have also been demonstrated as an intriguing host of strain-induced quantum-confined emitters with unique valley properties inherited from the host semiconductor. Here, we study the continuous and reversible tuning of the light emitted by such localized emitters in a monolayer tungsten diselenide embedded in a van der Waals heterostructure. Biaxial strain is applied on the emitters via strain transfer from a lead magnesium niobate–lead titanate (PMN-PT) piezoelectric substrate. Efficient modulation of the emission energy of several localized emitters up to 10 meV has been demonstrated on application of a voltage on the piezoelectric substrate. Further, we also find that the emission axis rotates by
Isolated spins are the focus of intense scientific exploration due to their potential role as qubits for quantum information science. Optical access to single spins, demonstrated in III-V semiconducting quantum dots, has fueled research aimed at realizing quantum networks. More recently, quantum emitters in atomically thin materials such as tungsten diselenide have been demonstrated to host optically addressable single spins by means of electrostatic doping the localized excitons. Electrostatic doping is not the only route to charging localized quantum emitters and another path forward is through band structure engineering using van der Waals heterojunctions. Critical to this second approach is to interface tungsten diselenide with other van der Waals materials with relative band-alignments conducive to the phenomenon of charge transfer. In this work we show that the Type-II band-alignment between tungsten diselenide and chromium triiodide can be exploited to excite localized charged excitons in tungsten diselenide. Leveraging spin-dependent charge transfer in the device, we demonstrate spin selectivity in the preparation of the spin-valley state of localized single holes. Combined with the use of strain-inducing nanopillars to coordinate the spatial location of tungsten diselenide quantum emitters, we uncover the possibility of realizing large-scale deterministic arrays of optically addressable spin-valley holes more »
- Publication Date:
- NSF-PAR ID:
- 10199856
- Journal Name:
- Nature Communications
- Volume:
- 11
- Issue:
- 1
- ISSN:
- 2041-1723
- Publisher:
- Nature Publishing Group
- Sponsoring Org:
- National Science Foundation
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as the magnitude of the biaxial strain is varied on these emitters. These results elevate the prospect of using all electrically controlled devices where the property of the localized emitters in a 2D host can be engineered with elastic fields for an integrated opto-electronics and nano-photonics platform. -
Abstract As hosts for tightly-bound electron-hole pairs carrying quantized angular momentum, atomically-thin semiconductors of transition metal dichalcogenides (TMDCs) provide an appealing platform for optically addressing the valley degree of freedom. In particular, the valleytronic properties of neutral and charged excitons in these systems have been widely investigated. Meanwhile, correlated quantum states involving more particles are still elusive and controversial despite recent efforts. Here, we present experimental evidence for four-particle biexcitons and five-particle exciton-trions in high-quality monolayer tungsten diselenide. Through charge doping, thermal activation, and magnetic-field tuning measurements, we determine that the biexciton and the exciton-trion are bound with respect to the bright exciton and the trion, respectively. Further, both the biexciton and the exciton-trion are intervalley complexes involving dark excitons, giving rise to emissions with large, negative valley polarization in contrast to that of the two-particle excitons. Our studies provide opportunities for building valleytronic quantum devices harnessing high-order TMDC excitations.
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