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The emergent electric field induced by pinned magnetic solitons remains poorly understood. Now the dissipative motion of magnetic domain walls under an alternating current in Weyl magnet NdAlSi devices is shown to induce a large emergent electric field.

Weyl semimetals are interesting because they are characterized by topological invariants, but specific examples discovered to date tend to have complicated band structures with many Weyl points. Here, the authors show that TaIrTe₄ has only four Weyl points, the minimal number required by time-reversal symmetry.

The tunability of the polarization state of light-emitting diodes (LEDs) based on conventional semiconductors is usually limited. Here, the authors report the realization of mid-infrared LEDs based on a Weyl semiconductor, layered Te, showing the electrical tunability of the degree of linear polarization of the emitted light from ~100% to 36%.

The topological character of electrons in semimetals subtly influences their bulk properties, leading typically to weak experimental signatures. Here, Moll et al. report a distinctive anomaly in the magnetic torque upon entering quantum limit state in the Weyl semimetal NbAs, which only appears due to the presence of Weyl fermions.

Here the authors experimentally demonstrate a maximally charged Weyl point in a three dimensional photonic crystal, with topological charge of four — the maximal charge number that a two-fold Weyl point can host, which supports quadruple-helicoid Fermi arcs

The study of lattice vibrations coupled to electronic excitations may provide an avenue for exploring exotic physical phenomena. Here, Xuet al. observe a Fano resonance in the Weyl semimetal TaAs, revealing evidence for a strong coupling between phonons and Weyl fermions.

Materials which simultaneously exhibit superconductivity and topologically non-trivial electronic band structure possess potential applications in quantum computing but have yet to be found. Here, the authors find superconductivity in MoTe₂, a material predicted to be topologically non-trivial.

Cooperative paramagnetism refers to a strongly correlated state without long range magnetic order that occurs in frustrated magnetic systems between the Neel temperature and Curie-Weiss temperature. Here, using resonant elastic magnetic and inelastic x-ray scattering, Terilli et al find a spectrally sharp gapped magnetic excitations that persists above the Neel temperature in Y₂Ir₂O₇, implying a cooperative paramagnetic phase.

2D Weyl semimetals are spin-polarized analogues of graphene that promise access to various topological properties of matter. Here, the authors evidence spin-polarized Weyl cones, Weyl nodes, and Fermi strings in monolayer bismuthene.

Surface Fermi arcs (SFAs) are characteristic features of a topological Weyl semimetal but there is no easy way to manipulate them so far. Here, the authors report manipulation of the shape, size and connections of SFAs in a Weyl semimetal NbAs, leading to an unusual topological Lifshitz transition.

Spin-momentum locking is a fundamental property of condensed matter systems. Here, the authors evidence parallel Weyl spin-momentum locking of multifold fermions in the chiral topological semimetal PtGa.

Here, the authors introduce a 3D Weyl metamaterial hosting modes bound to a 1D topological lattice defect. The modes carry nonzero orbital angular momentum locked to the direction of propagation, and they experimentally demonstrate the ability to emit acoustic vortices into free space.

Examples of materials with non-trivial band topology in the presence of strong electron correlations are rare. Now it is shown that quantum fluctuations near a quantum phase transition can promote topological phases in a heavy-fermion compound.

Weyl semimetals should exhibit unusual electronic behaviour but conditions where these effects dominate are difficult to achieve. Ramshaw et al. use high magnetic fields to drive TaAs into the quantum limit, finding evidence for the predicted chiral anomaly and an unanticipated increase in resistivity at the highest fields.

The Weyl fermions in NdAlSi mediate a helical incommensurate spin density wave, providing a rare example of Weyl-mediated collective phenomena.

Exotic transport properties of type-II Weyl semimetals have been predicted but are yet to be experimentally evidenced. Here, Li et al. report evidences of an anisotropy of negative magnetoresistance and a quantum oscillation arising from the predicted Weyl orbit in the type-II Weyl semimetal WTe₂.

Weyl semimetals exhibit Berry flux monopoles in momentum-space, but direct experimental evidence has remained elusive. Here, the authors reveal topologically non-trivial winding of the orbital-angular-momentum at the Weyl nodes and a chirality-dependent spin-angular-momentum of the Weyl bands, as a direct signature of the Berry flux monopoles in TaAs.

Systems with Weyl excitations can display very interesting physical phenomena. Here the authors demonstrate that Weyl excitations exist generically in 3D systems of dipolar particles following angular momentum transfer, and discuss how to observe them in cold alkaline-earth-atom systems.

The search for magnetic Weyl fermion remains a challenge. Here, the authors report angle-resolved photoemission spectroscopy and magnetotransport measurements resolving the topological properties of Weyl fermion quasiparticles in magnetic non-centrosymmetric crystal PrAlGe.

In all experimentally observed Weyl semimetals so far, the Weyl points always appear in pairs in the momentum space. Here, the authors report one unpaired Weyl point without surface Fermi arc emerging at the center of the Brillouin zone, which is surrounded by charged Weyl nodal walls in PtGa.

Despite various predictions, the evidence of Weyl fermions in oxide materials remains elusive. Here, the authors show evidence of Weyl fermions in quantum transport measurements in an epitaxial ferromagnetic oxide SrRuO₃.

Bulk band inversions in solids may unlock topological surface phenomena and symmetry-protected states. Here, the authors generate a surface state band inversion in the nonsymmorphic semimetal NbGeSb, leading to protected crossing points in the resulting spin-orbital entangled surface band structure.

Topological states may emerge in nonequilibrium but the mechanisms are much less understood. Here Topp et al. propose a nonequilibrium route to obtain the magnetic Weyl semimetallic phase in pyrochlore iridates by ultrafast modification of the effective electron-electron interactions with short laser pulses.

How electron correlation interplays with topological states remains rarely explored. Here, the authors report flat band arising due to electron correlations in magnetic Weyl semimetal Co₃Sn₂S₂ from a combined optical-spectroscopy and simulation study.

Candidate materials containing magnetic Weyl fermions remain rare. Here, the authors report evidence of a magnetic Weyl state and observe the surface Fermi arcs in YbMnBi₂.

In the charge-density-wave Weyl semimetal (TaSe₄)₂I, an axion is observed and identified as a sliding mode in the charge-density-wave phase characterized by anomalous magnetoelectric transport effects.

Topological states of matter with unique transport properties hold the potential to realize unexpected phenomena. Here, Aggarwalet al. report the coexistence of a superconducting phase and a high transport spin polarization at metallic point contacts on Weyl semimetal TaAs.

Optical second-harmonic waves are generated from the electric quadrupole contribution in a centrosymmetric magnetic Weyl semimetal Co₃Sn₂S₂. Two magnetic orders and phase transitions are explored in temperature-dependent rotational anisotropy measurements by second-harmonic generation.

The authors demonstrate ultrafast symmetry breaking by optically driven photocurrents.

Electronic correlation, geometric frustration, and topology are known to individually drive intriguing properties in materials. Here, the authors explore these interactions in the quasi-kagome Kondo Weyl semimetal Ce₃TiSb₅, revealing unconventional Hall effects that underscore the complex interplay of these factors, with implications for understanding topological and magnetic phenomena

Creating and controlling topological states of matter has become a central goal in condensed matter physics. Here, the authors report a predictive Floquet engineering of various topological phases in Na₃Bi by using femtosecond laser pulses.

Understanding the superconductivity in topological materials is of eminent interest. Here, Guguchia et al. report temperature-dependent magnetic penetration depth in the superconducting state of T _d -MoTe₂ under pressure, suggesting a topologically nontrivial s ⁺⁻ order parameter.

The evidence of topological origin for the recently observed anomalous Hall effect remains elusive. Here, the authors report that the resonance of the optical Hall conductivity resulted from topological electronic structure gives rise to the large intrinsic anomalous Hall effect in the magnetic Weyl semimetal Co₃Sn₂S₂.

Weyl fermions are evidenced in weakly correlated electron systems, but whether they survive strong electron correlations remains obscure. Here, Guo et al. report evidence of the chiral anomaly, topological Hall effect and a cubic temperature dependence of specific heat, suggesting existence of Weyl fermions in a heavy fermion semimetal YbPtBi.

Previous work has proposed that the anomalous and topological Hall effects, associated with Weyl nodes, should have a signature in optical conductivity. Here, using THz optical spectroscopy, the authors assign these two effects to optical conductivity resonances, arising near band anti-crossings, in thin films of MnGe.

An optical second-harmonic generation study of a series of transition metal monopnictide Weyl semimetals reveals a giant, anisotropic nonlinear optical response in these systems.

The Fermi arcs, topological surface states of Weyl semimetals can enable the intriguing spin control and facilitate topological spintronics. Here the authors report the spin-orbit torque at the interface of WTe₂/Py and attribute it to the enhanced spin accumulation by the spin-momentum locking effect of the Fermi arcs of WTe₂.

The half-Heusler GdPtBi is reported to exhibit negative longitudinal magnetoresistance. This is attributed to the chiral anomaly due to the formation of Weyl nodes with an applied magnetic field. The anomaly is also found to suppress the thermopower.

Topology and chirality of fermionic quasiparticles have enabled exciting discoveries, including quantum anomalous Hall liquids and topological superconductivity. Recently, topological and chiral phonons emerge as new and fast-evolving research directions. While these concepts are separately developed, they are intimately connected in the context of Weyl phonons. The couplings between chiral and topological phonons with various electronic and magnetic quasiparticles are predicted to give rise to new quantum states and giant magnetism with fundamental and applicational interests, ranging from quantum information science to dark matter detectors.

MoTe₂ is reported to host type II topological Weyl semimetal states. Two sets of Weyl points exist at different energies above the Fermi energy. Fermi arcs that form closed loops and are unique to type II Weyl semimetals are also found.

It has been predicted that the quasi-one-dimensional charge density wave material (TaSe₄)₂I hosts Kramers-Weyl fermions, but direct spectroscopic evidence of this is limited. Here, ARPES and theoretical calculations reveal signatures that may indicate the presence of Kramers-Weyl fermions.

Weyl fermions have yet to be observed as elementary particles but can be realized in topological quantum materials. This Review discusses the theoretical and experimental discovery of emergent Weyl fermions, high-fold chiral fermions, topological Weyl lines and related Dirac phases.