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The authors study the non-centrosymmetric achiral material In_xTaS₂ by angle-resolved photoemission spectroscopy and quantum oscillations. They find that it hosts an “ideal” Kramers nodal line, well isolated at the Fermi level.

A scanning tunnelling microscopy study demonstrates that one-dimensional charge density waves can form at twin boundaries in a monolayer transition metal dichalcogenide.

The transition from an indirect to direct bandgap in transition metal dichalcogenides has been observed in samples with thicknesses ranging from 8 to 1 monolayers by angle-resolved photoemission spectroscopy.

Whether electron–phonon coupling is a generic feature in FeSe/SrTiO₃ to enhance superconductivity remains unclear. Here, Zhang et al. report replica bands in FeSe/SrTiO₃(110), suggesting a common mechanism in FeSe on SrTiO₃with different surface terminations.

The interplay between reduced dimensionality and interactions in monolayer transition metal dichalcogenides has been of great research interest. Here the authors report an insulating dimer ground state in 1T-IrTe₂, driven by the combined effect of the charge density wave instability and local atomic bond formation.

What happens to correlated electronic phases—superconductivity and charge density wave ordering—as a material is thinned? Experiments show that both can remain intact in just a single layer of niobium diselenide.

Transition metal dichalcogenides are attracting widespread attention for their appealing optoelectronic properties. Using a combination of numerical and experimental techniques, the exciton binding energy is now determined for MoSe₂ on graphene.

The nature of defects in transition metal dichalcogenide semiconductors is still under debate. Here, the authors determine the atomic structure and electronic properties of chalcogen-site point defects common to monolayer MoSe₂ and WS₂, and find that these are substitutional defects, where a chalcogen atom is substituted by an oxygen atom, rather than vacancies.

A combination of photoemission and scanning tunnelling spectroscopy measurements provide compelling evidence that single layers of 1T'-WTe₂ are a class of quantum spin Hall insulator.

Previous work proposed the Berry curvature dipole as the mechanism of the nonlinear Hall effect. Lee et al. establish the sign-changing Berry curvature hot spots from spin-orbit split bands as the origin of the Berry curvature dipole and link it to the nonlinear Hall effect in the topological semimetal NbIrTe₄.

The bulk conductivity of a topological insulator composed of Bi, Sb and Te can be reduced by orders of magnitude by tuning the ratio of Bi to Sb, allowing surface states to dominate conduction.

ARPES measurements of the ‘failed’ superconductor LBCO-1/8 suggest that its pseudogap phase consists of two distinct components. The result could be an important clue into the nature of this phase in the copper oxide superconductors.

Transition metal dichalcogenides may host exotic topological phases in the two-dimensional limit, but detailed atomic properties have rarely been explored. Here, Ugeda et al. observe edge-states at the interface between a single layer quantum spin Hall insulator 1T′-WSe₂ and a semiconductor 1H-WSe₂.

The controlled manipulation of the topological phases of electronic materials is a central goal of modern condensed matter research. Here, the authors demonstrate controllable switching between two distinct topological phases in a layered ferromagnet via thermal cycling.

Signatures of an excitonic insulator have been reported in several two-dimensional materials. Here the authors report electronic properties of monolayer ZrTe₂ from ARPES and STM measurements that are consistent with the preformed exciton gas phase, a precursor for the excitonic insulator.

Over the last few years, several van der Waals materials have been found that retain magnetic ordering down to monolayer thickness. These materials provide a simple platform for studying the magnetism in reduced dimensions. Here, Zhong et al study the thickness dependence of magnetic ordering in Cr2Te3, and find a crossover from Stoner to Heisenberg-type magnetism as thicknesses are reduced.

The electrons that contribute to the Mott insulator state in single-layer 1T-TaSe2 are shown to also have a rich variation in their orbital occupation. As more layers are added, both the insulating state and orbital texture weaken.

Unconventional quasiparticles carrying spin but not electric charge emerge in quantum spin liquid phases. The Kondo interaction of these spinon quasiparticles with magnetic impurities may now have been observed.

Stacking graphene in such a way that each layer is rotated relative to the one below provides a way of controlling the properties of this useful material. Park et al. now demonstrate a technique for fabricating this twisted graphene in such a way that it has an intrinsic electronic bandgap.

Some quantum spin liquids are expected to have an effective Fermi surface of fractionalized spinon excitations. The two-dimensional spin liquid candidate 1T-TaSe₂ has charge density modulations that may be caused by an unstable spinon Fermi surface.

An electrically controlled phase transition from topological insulator to conventional insulator in ultrathin films of the topological Dirac semimetal, Na₃Bi.

The underlying mechanism of iron-based superconductivity, the role of electron correlations, and the extent to which the behavior resembles those of the cuprates has been debated since their discovery. Here, using angle resolved photoemission spectroscopy, the authors report reconstruction of the Fermi surface for FeTe_1−xSe_x driven by orbital-dependent correlation effects in the absence of symmetry breaking and find evidence for an orbital-selective Mott transition.

The emergence of quasiparticles in a doped Mott insulator is the key to understanding high Tc cuprate superconductivity - a major quest in condensed matter physics. Here, the authors investigate the angle-resolved photoemission spectroscopy in the cuprates and observe how the quasiparticle emerges from the Mott insulating regime.