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Here, the authors use a tapered optical fibre to create a dynamic, reversible strain in a suspended WSe₂ monolayer, and observe that dark excitons are funnelled to high-strain regions and are the principal participants in drift and diffusion at cryogenic temperatures.

Single atomic layers of transition metal dichalcogenides are semiconductors with possible applications in spintronics. Here, the authors demonstrate tuning of the spin-orbit splitting in molybdenum tungsten diselenide by altering the alloy’s composition, impacting valley polarization and light emission yield.

The valley index of an electron is a magnetic moment that can be initialized optically and probed electrically. Now, experiments reveal how magnetic fields can break the degeneracy for states with different valley indices.

Time-resolved measurements of the exciton dynamics in tungsten diselenide monolayers reveal ultrafast radiative recombination of the exciton ground state (∼150 fs) and the interplay between optically bright and dark excitons.

Spin coherence of valence holes in semiconductor quantum-dots is governed by interactions with the nuclear spins of the dot lattice. Experiments and theory have revealed an important new ingredient that determines the strength and sign of this coupling.

Four studies demonstrate the vast opportunities provided by stacking pairs of monolayer materials and changing the resulting optical properties by twisting one material with respect to the other.

Ultrafast laser fields are able to widely tune the physical properties of semiconductors by generating virtual states. Using strong fields at energies below the optical bandgap, control of excitons in two-dimensional semiconductors has now been demonstrated.

Interlayer excitons in bilayer MoS₂ exhibit both a high oscillator strength and highly tunable energies in an applied electric field.

Efficient second-harmonic generation (SHG) occurs for crystals with broken inversion symmetry, such as transition metal dichalcogenide monolayers. Here the authors show SHG tuning in bilayer MoS₂ - an inversion-symmetric crystal - mediated by interlayer excitons.

The primary stages of carrier relaxation in atomically thin transition metal dichalcogenides are hardly accessible due to their fast timescales. Here, the authors measure the first stages of carrier–phonon interaction in monolayer WSe₂ via a series of periodic maxima in the hot photoluminescence intensity, assigned to phonon cascades.

The authors investigate the interplay between the stacking order and the interlayer coupling in MoS₂ homobilayers as well as artificially stacked bilayers grown by chemical vapour deposition, and identify the interlayer exciton absorption and A-B exciton separation as indicators for interlayer coupling.

Here, the authors discover the ground and excited state interlayer excitons in bi- and tri-layer 2H-MoSe₂ crystals which exhibit electric-field-driven hybridisation with the intralayer A excitons, showing distinct spin, layer and valley characteristics.

Enhancing and tuning light-matter interactions is crucial for the advancement of future technologies; however, to achieve this, it is essential to find materials that are compatible with CMOS technology. In this study, the authors demonstrate that coupling a MoSe2 monolayer with a silicon-based dielectric nanoresonator can enhance and tune the absorption of the former to near-field resonances.

Here, the authors use tip-enhanced photoluminescence spectroscopy to show a discontinuity of the exciton density distribution on each side of the interface of a MoSe₂/WSe₂ lateral heterostructure. They introduce the concept of ‘exciton Kapitza resistance’ by analogy with the interfacial thermal resistance known as ‘Kapitza resistance’.

The authors unveil the many-particle processes underpinning the formation of bound charge transfer excitons at the interface of hBN-encapsulated lateral MoSe₂-WSe₂ heterostructures. The excitons can be tuned via interface (i.e. high quality lateral junction) and dielectric (i.e. hBN encapsulation) engineering.

Optical excitation of transition metal dichalcogenide monolayers mostly generates excitons species with inherently short lifetime and spin/valley relaxation time. Here, the authors demonstrate efficient spin/valley optical pumping of resident electrons in n-doped WSe₂ and WS₂ monolayers.

Understanding light–matter interactions in layered materials is crucial for applications in photonics and optoelectronics. This Technical Review discusses the optical spectroscopy techniques to access details of the electronic band structure, crystal quality, crystal orientation and spin–valley polarization, including key aspects of practical set-ups to perform experiments for a broad range of applications.

Excitons, quasi-particles of tightly bound electron-hole pairs, dominate the optical response of atomically thin transition metal dichalcogenides. Here, the authors review strong light-matter coupling in two-dimensional semiconductors arising from confined excitons interacting with trapped photons or localized plasmons.