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The family of topological materials has been growing rapidly but most members bare limitations hindering the study of exotic behaviour of topological particles. Here, Schoop et al. report a Fermi surface with a diamond-shaped line of Dirac nodes in ZrSiS, providing a promising candidate for studying two-dimensional Dirac fermions.

Most of the notable properties of graphene are a result of the cone-like nature of the points in its electronic structure where its conduction and valance bands meet. Similar structures arise in 2D HgTe quantum wells, but without the spin- and valley-degeneracy of graphene; their properties are also likely to be easier to control.

The magnetoresistance suggests an exotic topological phase in LaBi, but the evidence is still missing. Here, Nayaket al. report the existence of surface states of LaBi through the observation of three Dirac cones, confirming it a topological semimetal.

The existence of a topological bulk-boundary correspondence for Dirac semimetals has remained an open question. Here, Wieder et al. predict one-dimensional hinge states originating from bulk three-dimensional Dirac points in solid-state Dirac semimetals, revealing condensed matter Dirac fermions to be higher-order topological.

The alloy bismuth-palladium is a candidate material for observing topological superconductivity. Here, the authors study the interplay of spin–orbit interactions and superconductivity in this noncentrosymmetric compound using scanning tunnelling spectroscopy and relativistic first-principles calculations.

The opening of a Dirac point gap in topologically non-trivial materials is key to potential applications. Here, the authors use photoelectron spectroscopy to study gap formation and carrier mass acquisition in a topological crystalline insulator as a function of composition and temperature.

The interactions of quasiparticles can be described by renormalizing their masses, such that some materials have a vanishingly small effective mass, whereas others have a very high effective mass. The observation by Vyalikh and colleagues of both extremes occurring on the surface and interior of the same material offers a new view of many-body interactions.

Novel physics of topological aspects are obscured due to lack of effective way to manipulate topological particles. Here, Xu et al. demonstrate independent control of Dirac fermions on top and bottom surfaces of BiSbTeSe₂flakes by dual-gating, which suggests a way to manipulate exotic particles.

In graphene and on the surfaces of many topological insulators, the Dirac cones are pinned to high symmetry points in reciprocal space. Here, the authors report that the Dirac cones in atomically-thin Sb layers occur at generic reciprocal-space points which can be tuned by lattice strain.

In theory, the anomalous quantum Hall effect is observed in edge channels of topological insulators when there is a magnetic energy gap at the Dirac point; this gap has now been observed by low-temperature photoelectron spectroscopy in Mn-doped Bi₂Te₃.

The excited states of three-dimensional topological insulators can be accessed by ultrafast light pulses, which opens new possibilities for current transmission. Here, the authors show that a non-equilibrium gas of relativistic fermions with a long lifetime can emerge in a photoexcited topological insulator.

The authors study a liquid crystal microcavity with polarization-dependent absorption, a source of non-Hermiticity. The transition in the Hermitian topology of the spin-orbit coupling makes possible the annihilation of exceptional points.

Topological defects and textures are universal phenomena across physics. The authors demonstrate that an initial non-singular spinor texture can be controllably transformed into a pair of singular vortices with cores filled by atoms that continuously connect distinct magnetic phases of matter.

Type-I and type-II bulk Dirac cones and ladders of topological surface states are shown to form in six different transition-metal dichalcogenides.

Topological surface states in lead-doped tin selenide are assumed to arise from massive Dirac states in the bulk, but this has not been demonstrated to date. Using thermoelectric transport measurements, Liang et al.now close this gap, and further show a sign anomaly in the Nernst signal due to band inversion.

Magnetic symmetry is a vital factor to determine exotic topological phases. Here, Riberolles et al. demonstrate a helical antiferromagnetic order in EuIn₂As₂ which makes it a magnetic topological-crystalline axion insulator.

Quantum spin liquids can emerge in frustrated magnets where quantum fluctuations prevent long-range order. Seifert et al. show that spin-lattice couplings can relieve magnetic frustration and destabilise 2D gapless quantum spin liquid states with fractionalised excitations, analogous to the 1D spin-Peierls instability.

The spin texture in presence of both inversion and time-reversal symmetries has been difficult to observe. Here, Nakamura et al. report evidence of hidden entanglement between spin and momentum in antiperovskite Dirac material Sr₃SnO.

Two-dimensional massive and massless Dirac fermions in HgTe/CdHgTe quantum wells yield terahertz Landau emission. The emission frequency is continuously tunable with magnetic field or carrier concentration, over the range from 0.5 to 3 THz.

Each valley of the mini-Brillouin zone ("mini valley") of twisted bilayer graphene (TBG) contains two Dirac cones that hybridize to form flat bands. Theory predicts that these two Dirac cones have the same chirality, leading to topological obstruction. Here, the authors confirm this prediction experimentally.

The terahertz response of topological insulator surface states, in which relativistic electrons are protected from backscattering, possesses potential optic and plasmonic applications. Here, the authors demonstrate a nonlinear absorption response of Bi₂Se₃to terahertz electric fields.

In topological insulators, topology imposes a quantum phase transition between the trivial and nontrivial phases. Here, Xu et al. demonstrate how properties of the topological surface states emerge in the trivial phase of BiTl(S_1-δSe_δ)₂when close to its chemically tuned phase transition.

Leggett modes can occur when superconductivity arises in more than one band in a material and represent oscillation of the relative phases of the two superconducting condensates. Now, this mode is observed in Cd₃As₂, a Dirac semimetal.

A state of matter known as a three-dimensional Dirac semimetal has latterly garnered significant theoretical and experimental attention. Using angle-resolved photoelectron spectroscopy, it is shown that Cd₃As₂ is an experimental realization of a three-dimensional Dirac semimetal that is stable at ambient conditions.

The transport behavior at the quantum limit may show exotic phenomena such as special interlayer quantum transport. Here, the authors observe negative interlayer magnetoresistance resulted from tunneling of Dirac fermions between the zeroth Landau levels in BaGa₂, indicating a feature at the quantum limit.

BiTeCl is a topological insulator with strong inversion asymmetry, which exhibits bulk charge polarization and pyroelectricity. Such a long-sought topological insulator paves the way for applications involving natural p–n junctions and spintronics.

The detection of topological states is restricted to limited experimental tools. Here, the authors apply broadband solid-state ¹²⁵Te nuclear magnetic resonance on Bi₂Te₃ nanoplatelets uncovering signals distinguishing edge Dirac electrons and bulk electrons.

Local electronic compressibility measurements of magic-angle twisted bilayer graphene show that the insulating and superconducting phases of this system are both derived from a high-energy symmetry-broken state.

Plasmonic excitation of massless electrons is observed in Bi₂Se₃.

Dirac semimetals are 3D materials where the conduction and valence bands meet at what are called Dirac points. The author shows that almost all the properties inherent in the Dirac semimetals are exhibited by a wider class of materials that need not have the gapless Dirac points.

The lack of band gap controllability in graphene severely restricts its use in nanoelectronics. Here, the authors predict that post-graphene organic Dirac materials should allow for exceptional electronic tunability between graphene-like semimetallicity and multi-radical and/or closed-shell semiconducting states.

A combination of detailed photoelectron spectroscopy measurements and numerical simulations reveal the presence of so-called Dirac node arcs in the electronic structure of PtSn₄.

Graphene’s linear dispersion relation makes its charge carriers behave as if they were massless. However, near the Dirac point where graphene’s valence and conduction bands meet, electron–electron interactions cause this relation to diverge, such that it becomes strongly nonlinear and the effective carrier velocity doubles.

In this work, researchers build a scalable photonic Chern insulator by twisting a fibre during fabrication, breaking an effective time-reversal symmetry and inducing a pseudo-magnetic field. The team reveals a ‘Goldilocks’ regime that guarantees topological protection against fabrication-induced disorder of any symmetry class in the fibre cross-section.

Magnetic monopoles have for a long time eluded detection by experiment. Theory now identifies a signature of monopole dynamics that is measurable experimentally, and that has already been seen in magnetic relaxation measurements in a spin-ice material.

Three-dimensional analogues of graphene have recently been synthesized. The transport properties of such a Dirac semimetal, Cd₃As₂, have been studied, revealing an unexpected mechanism that suppresses backscattering dramatically.

Despite their name, the bulk electrical conductivity of most topological insulators is relatively high, masking many of the important characteristics of its protected, surface conducting states. Counter-doping reduces the bulk conductivity of Bi₂Se₃ significantly, allowing these surface states and their properties to be clearly identified.