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The valley Hall effect in 2D materials is a promising approach for future valleytronic applications, but it is usually based on excitons with short lifetimes. Here, spin polarized electrons are injected from WTe₂ into MoS₂, leading to a unipolar valley Hall effect with enhanced lifetimes and mobility.

The standard topological insulator is characterized by an insulating bulk and a conducting boundary, so a three dimensional insulating bulk of a topological insulator has a conducting surface. Recently, this idea was extended to the edges of the surfaces of the three dimensional material as a new topological phase, referred to as a higher-order topological insulator. Here, the authors find evidence of such higher order topological insulator states in tungsten ditelluride using heterostructures composed of tungsten ditelluride and graphene.

The optical Stark effect is a light-matter interaction phenomenon that can be used to address and control exciton states in semiconductors. Here, the authors achieve optical tuning of the Stark effect of an individual exciton state in few-layer ReS₂with varying light polarization.

Single atomic layers of transition metal dichalcogenides have outstanding electrical and optical properties. Here, the authors show that light absorption and emission from stacks of different transition metal dichalcogenide monolayers can be tuned by rotating the crystals.

Few-layer molybdenum ditelluride and tungsten diselenide field-effect transistors can be reversibly doped with different carrier types and concentrations using pulses of ultraviolet and visible light, allowing reconfigurable complementary metal–oxide–semiconductor circuits to be created.

A laser can be used to locally dope two-dimensional molybdenum ditelluride channels, allowing both n- and p-doped channels to be assembled within the same atomic plane and for device arrays of n–p–n bipolar junction transistor amplifiers and radial p–n photovoltaic cells to be fabricated.

Excitons—bound electron-hole pairs—in two-dimensional transition-metal dichalcogenides can exhibit a rich spectrum of excited states. Here, the authors use ultrafast mid-infrared spectroscopy to explore the dynamics of these so-called 1s-intraexcitonic transitions in monolayer molybdenum disulphide.

Under strong laser fields, materials exhibit extreme non-linear optical response, such as high harmonic generation. These higher harmonics provide insights into electron behaviour in materials in sub-laser cycle timescale. Here, Cha et al study higher harmonic generation resulting from the laser driven motion of massless Dirac fermions in graphene.

Lateral TMD–graphene–topological insulator hetero-devices enable room-temperature optoelectronic transport of the valley-locked spin polarization degree of freedom.

Quantum beats are periodic oscillations originating from the superposition of coherent quantum states. Here, the authors observe exciton quantum beats in the optical spectrum of atomically thin ReS₂, and modulate the intensity of the quantum beat signal by means of light polarisation.

Correlated insulator states of moire excitons in transition metal dichalcogenide heterostructures have attracted significant attention recently. Here the authors use time-resolved pump-probe spectroscopy to demonstrate the effects of non-equilibrium correlations of moire excitons in WSe₂/WS₂ heterobilayers.

Vertical integration of two-dimensional materials can open unprecedented possibilities towards design of efficient optoelectronic devices. Here, the authors investigate the photoresponse properties of a graphene/MoS₂/graphene heterostructure, revealing promising quantum efficiency performances.

For optical control of plasmons metals require a large amount of power in the control pulse, yielding a small modulation depth. Here, Sim et al. fabricate arrays of Bi₂Se₃ and report a modulation depth of 2,400% at 1.5 THz with an optical fluence of 45 μJ/cm², demonstrating a novel route for controlling plasmons.

Geometric confinement on arbitrary substrates promotes, without epitaxial seeding, the layer-by-layer growth of two-dimensional single-crystal monolayers and bilayers of transition metal dichalcogenides.

Here, the authors report the observation of deep-ultraviolet (DUV) electroluminescence and photocurrent generation in van der Waals heterostructures based on hBN crystals, showing potential for DUV light emitting and detection devices.

Kinetics-controlled van der Waals epitaxy in the near-equilibrium limit by metal–organic chemical vapour deposition enables precise layer-by-layer stacking of dissimilar transition metal dichalcogenides.

Transition metal dichalgogenide sheets prepared by liquid phase exfoliation can be limited in terms of scalability. Here, Velusamy et al. use a scalable liquid phase exfoliation process to fabricate micrometre thick composite nanosheets with amine-terminated polymers, which exhibit photo-detective properties.