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Fractional Chern insulators have been observed in moiré MoTe₂ at zero magnetic field, but the expected zero longitudinal resistance has not been demonstrated. Now it is shown that improving device quality allows this effect to appear.

Topological materials hold great promise for dissipationless information transmission. Here, the authors create Chern insulator junctions between domains with different Chern numbers in MnBi₂Te₄ to realize the basic operation of a topological circuit.

In analogy with quantum Hall systems, it may be possible to find non-abelian anyons in the higher bands of Chern insulators. Now, the phase diagram of the second moiré band of twisted MoTe₂ is explored, laying the groundwork for such investigations.

Single layers of group-VI transition metal dichalcogenides have emerged as direct bandgap semiconductors in the two-dimensional limit. The authors show that monolayer molybdenum diselenide is an ideal system enabling electrostatic tunability of charging effects in neutral and charged electron-hole pairs, so-called excitons.

Pressure-induced changes in the magnetic order of bilayer and trilayer van der Waals crystals are revealed and attributed to changes in the stacking arrangement.

Exciton condensation has been observed in various three-dimensional (3D) materials. Now, monolayer WTe₂—a 2D topological insulator—also shows the phenomenon. Strong electronic interactions allow the excitons to form and condense at high temperature.

Electrical control of magnetism in a bilayer of CrI₃ enables the realization of an electrically driven magnetic phase transition and the observation of the magneto-optical Kerr effect in 2D magnets.

The nature of the insulator-metal phase transition in VO₂ remains elusive. Using pump-probe spectroscopy and near-field imaging, O’Callahan et al. study the ultrafast dynamics of many micro-crystals and find an inhomogeneous response, highlighting the importance of microscopic perturbations to the transition.

Transport measurements in twisted bilayer MoTe₂ reveal quantized Hall resistance plateaus and composite Fermi liquid-like behaviour under zero magnetic field, constituting a direct observation of integer and fractional quantum anomalous Hall effects.

Exotic states emerge from the interplay between band topology and ferromagnetism, but it remains less known in canted-antiferromagnetic phase. Here, the authors realize a canted-antiferromagnetic Chern insulator in atomically-thin MnBi₂Te₄ with electrical control of chiral-edge state transport.

Recent experiments have shown the formation of ferroelectric domains in twisted van der Waals bilayers. Here, the authors report near-field infrared nano-imaging and nano-photocurrent measurements to investigate ferroelectricity in minimally twisted WSe₂ by visualizing the plasmonic and photo-thermoelectric response of an adjacent graphene monolayer.

Metallic ferromagnetism is reported in an exfoliated monolayer of the van der Waals material Fe₃GeTe₂.

Many strongly correlated electron systems have a domain structure that obscures the fundamental properties of the homogeneous material. Experiments on single-domain nanobeams made of vanadium dioxide have revealed several new aspects of the metal–insulator transition in this material.

Experiments showing that a single layer of WTe₂ can conduct electricity along its edges while insulating in the interior suggests that this material is a two-dimensional topological insulator.

The coupling between magnetism and topology is studied in a van der Waals heterostructure.

Physical vapour transport is now used to grow single-atomic-layer lateral MoSe₂/WSe₂ heterojunctions, enabling the development of in-plane architectures for optoelectronic applications based on these semiconducting materials.

Charge transfer from adsorption is shown to provide an electrical method for probing the collective behaviour of atoms and small molecules confined to the surface of a carbon nanotube.

Stacking a monolayer and bilayer of graphene, with a small twist angle between them, creates a tunable platform where the physics of both twisted bilayer graphene and twisted double bilayer graphene can be realized.

When laser light is focused onto graphene devices in a magnetic field a long-range photo-Nernst effect causes photocurrents to be generated along the free edges.

The precise location of a solid-state triple point, at which three solid phases coexist in thermal equilibrium, has been determined by controlling the stress and temperature in a nanobeam of vanadium dioxide near its metal–insulator transition.

Atomically thin chromium tri-iodide is shown to be a 2D ferromagnetic insulator with an optical response dominated by ligand-field transitions, emitting circularly polarized photoluminescence with a helicity determined by the magnetization direction.

Alcoholic drinks were consumed in larger quantities in the eighteenth and nineteenth centuries than in the twentieth century, although there has been a recent increase from the historical low of 1930–60. Beer, spirits and wines once provided at least 2 MJ (nearly 500 kcal) per person per day compared with 0.67 MJ (160 kcal) in 1975, towards an average energy requirement of the total population little different from that needed now. Beer has always contributed most to the alcohol, energy and nutrient content of the diet, although its importance relative to spirits and wine has declined.

Photocurrent microscopy on suspended vanadium dioxide nanobeams reveals the thermal origin of the photoresponse in materials with strong electron–electron and electron–phonon correlations.

Bright and electrostatically tunable electroluminescence from monolayer WSe₂ p–n junctions is reported.

Hot carriers dominate energy transport across graphene p–n junctions that are excited by ultrafast laser pulses, and set fundamental limits on device speeds.

Two- and three-layer WTe₂ exhibits spontaneous out-of-plane electric polarization that can be switched electrically at room temperature and is sufficiently robust for use in applications with other two-dimensional materials.

The behaviour of Tungsten ditelluride (WTe2) in few-layer form is not yet fully characterized. Here the authors use a near-field terahertz microscopy technique to observe the electromagnetic responses of WTe2 flakes from one to several layers and to study their semimetallic/ semiconducting behavior.

Physicists are investigating phenomena at ever smaller scales. One example comes from work on the ‘Aharonov-Bohm effect’, the quantum mechanical influence of a magnetic field on electron motion — the effect has now been shown to occur in a carbon nanotube, illustrating the potential for doing basic physics with single molecules.

Changes in the electronic states of two-dimensional semiconductor devices resulting from electrical gating can be monitored directly using micrometre-scale angle-resolved photoemission spectroscopy.

It is not easy finding a worthy successor to highly refined microchip technologies. But electronic devices built from molecular-scale components are fast becoming a good bet.

Magneto-optical Kerr effect microscopy is used to show that monolayer chromium triiodide is an Ising ferromagnet with out-of-plane spin orientation.

Excitonic valley quantum coherence is optically generated and detected by polarization-resolved photoluminescence spectroscopy in the monolayer semiconductor WSe₂.

One way of producing Majorana fermions for topological quantum computing is to induce superconductivity in other topological states. Here, the proximity effect does this for the quantum spin Hall effect state in a 2D material.

An upconversion from negatively charged to neutral excitons is observed in monolayer tungsten diselenide, which could provide a route for cooling two-dimensional semiconductors using lasers.

Monolayer and few-layer materials present interesting spin and pseudospin states. A study of the coupling between spin, valley and layer degrees of freedom in bilayer WSe₂ reveals coherent superpositions of distinct valley configurations and suggests the possibility of electrical control of the spin states.

Research on two-dimensional van der Waals ferroelectrics has witnessed an explosion over the past few years. This Perspective formulates a framework by which results can be analysed, reviews recent progress, discusses mechanisms and properties for applications, and outlines challenges to be addressed.