Karol Nogajewski

Single photon emitters in exfoliated WSe2 structures.

Crystal structure imperfections in solids often act as efficient carrier trapping centres, which, when suitably isolated, act as sources of single photon emission. The best known examples of such attractive imperfections are well-width or composition fluctuations in semiconductor heterostructures (resulting in the formation of quantum dots) and coloured centres in wide-bandgap materials such as diamond. In the recently investigated thin films of layered compounds, the crystal imperfections may logically be expected to appear at the edges of commonly investigated few-layer flakes of these materials exfoliated on alien substrates. Here, we report comprehensive optical micro-spectroscopy studies of thin layers of tungsten diselenide (WSe2), a representative semiconducting dichalcogenide with a bandgap in the visible spectral range. At the edges of WSe2 flakes (transferred onto Si/SiO2 substrates) we discover centres that, at low temperatures, give rise to sharp emission lines (100 μeV linewidth). These narrow emission lines reveal the effect of photon antibunching, the unambiguous attribute of single photon emitters. The optical response of these emitters is inherently linked to the two-dimensional properties of the WSe2 monolayer, as they both give rise to luminescence in the same energy range, have nearly identical excitation spectra and have very similar, characteristically large Zeeman effects. With advances in the structural control of edge imperfections, thin films of WSe2 may provide added functionalities that are relevant for the domain of quantum optoelectronics.

Brightening of dark excitons in monolayers of semiconducting transition metal dichalcogenides

We present low temperature magneto-photoluminescence experiments which demonstrate the brightening of dark excitons by an in-plane magnetic field

Landau Level Spectroscopy of Electron-Electron Interactions in Graphene

B

Exciton band structure in layered MoSe2: from a monolayer to the bulk limit

applied to monolayers of different semiconducting transition metal dichalcogenides. For both WSe

Radiatively Limited Dephasing and Exciton Dynamics in MoSe2 Monolayers Revealed with Four-Wave Mixing Microscopy

_2

Optical properties of atomically thin transition metal dichalcogenides: observations and puzzles

and WS

Raman scattering of few-layers MoTe2

_2

Rhombohedral Multilayer Graphene: A Magneto-Raman Scattering Study

monolayers, the dark exciton emission is observed at

The optical response of monolayer, few-layer and bulk tungsten disulfide

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Sub-bandgap Voltage Electroluminescence and Magneto-oscillations in a WSe2 Light-Emitting van der Waals Heterostructure

50 meV below the bright exciton peak and displays a characteristic doublet structure which intensity is growing with