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The authors identify two coexisting incommensurate charge density waves whose interplay leads to joint commensuration and a long-period moiré structure.

It is generally assumed that modulating magnetic properties via linear excitations of Raman-active phonons is forbidden in inversion symmetric magnets. Here, Luo, Ning, Ilyas, von Hoegen, and coauthors demonstrate a linear excitation of Raman-active lattice vibrations, via magnon-polaron excitation.

Emergent phenomena at the interface between a topological insulator and a ferromanget reflect broken symmetry of topological state. Here, Lee et al. report direct measurement of induced magnetism at the Bi₂Se₃-EnS interface, paving the way to understand emergent orders in topological material with broken time reversal symmetry.

Van der Waals materials can exhibit strong coupling between the lattice and other degrees of freedom. Here, Ergeçen et al reveal the presence of bound states emerging from the strong interaction between the lattice vibrations and d-orbitals in the van der Waals antiferromagnet NiPS₃.

Previous work has shown the existence of spin-orbit-entangled excitons and their coupling to antiferromagnetism in the correlated insulator NiPS₃. Here the authors show that non-equilibrium driving of these excitons produces a transient metallic antiferromagnetic state that cannot be achieved by tuning the temperature in equilibrium.

Monolayer graphene has been long proposed as a candidate system for Floquet engineering. Time- and angle-resolved photoemission spectroscopy measurements now show the formation of Floquet–Bloch states in this material.

Measuring and characterizing dynamic charge density waves in cuprate superconductors is a challenging task. By using a method based on ultrafast spectroscopy, the problem is overcome and detecting the presence and lifetimes of these fluctuations is made possible.

Experimental observations and theoretical analysis provide evidence that the spin polarization of the spin-spiral type II multiferroic NiI₂ exhibits p-wave magnetism and its spin chirality is related to ferroelectric polarization, which can be electrically controlled. 

Intense terahertz pulses are used to induce metastable magnetization with a remarkably long lifetime of more than 2.5 milliseconds in a van der Waals antiferromagnet, FePS₃.

Second-order superlattices emerge from the interference between moiré superlattices of comparable periodicities. Direct real-space visualization reveals their rich structural diversity and extreme sensitivity to external parameters such as strain and twist angle.

The interplay between charge density wave states in emerging kagome superconductors is a topic of ongoing debate. Here, the authors unveil the out-of-equilibrium competition between two coexisting charge density waves in CsV₃Sb₅ by harnessing time-resolved X-ray diffraction.

A photocurrent enhancement at the charge neutrality point is observed in graphene when the Fermi level matches the Dirac point.

Interlayer transport can be made to occur slower or faster than intralayer scattering in van der Waals heterostructures, allowing the thermalization pathways for optically excited carriers to be tuned.

Polaritons, light-matter hybridized quasiparticles, are the fundamental excitation of strong coupling systems and are widely applicable in information technologies. Here the authors applied the concept of time-of-flight measurement in terahertz induced second harmonic generation experiments in various systems to comprehensively study the dispersion relation of phonon-polaritons and reveal potential spin-lattice couplings.

Optical chiral induction and spontaneous gyrotropic electronic order are realized in the transition-metal chalcogenide 1T-TiSe₂ by using illumination with mid-infrared circularly polarized light and simultaneous cooling below the critical temperature.

Short pulses of light shift the balance between two competing charge density wave phases, allowing the weaker one to manifest transiently while suppressing the stronger one. This shows that competing phases can be tuned in a non-equilibrium setting.

Three different ultrafast probes investigate a non-adiabatic phase transition and find substantial evidence of topological defects inhibiting the reformation of the equilibrium phase.

Time- and angle-resolved photoelectron spectroscopy experiments are used to monitor the transition between Floquet–Bloch and Volkov states in the topological insulator Bi₂Se₃.

The lifting of valley degeneracy in the monolayer transition metal dichalcogenide WS₂ is now demonstrated by the optical Stark effect, showing that each valley can be selectively tuned by up to 18 meV.

Manipulating collective phenomena in solid-state platforms with optical means is an ongoing topic of interest in condensed matter physics. Here, the authors demonstrate all-optical room-temperature manipulation of electronic states in the charge-density-wave material EuTe₄.

Using several ultrafast diffraction and microscopy techniques, demagnetization-driven interlayer shear of a van der Waals antiferromagnet is visualized at the nanoscale.

Currently, it is difficult to reach high momenta with narrow energy resolution via laser-based angle-resolved photoemission spectroscopy (ARPES). Here, Sie et al. develop a time-resolved XUV based ARPES setup which can access the first Brillouin zone of all materials with narrow energy resolution.

Electronic ferroelectricity is observed in a graphene-based moiré heterostructure, which is explained using a spontaneous interlayer charge-transfer model driven by layer-specific on-site Coulomb repulsion.

Van der Waals materials are characterized by two dimensional layers weakly held together by interlayer van der Waals forces. Here, the authors study how shear motions between these layers influence the magnetic properties of the van der Waals antiferromagnets FePS3, MnPS3, and NiPS3. ‘

Multiple complementary optical signatures confirm the persistence of ferroelectricity and inversion-symmetry-breaking magnetic order down to monolayer NiI₂, introducing the physics of type-II multiferroics into the area of van der Waals materials.

The nonlinear Hall effect is observed in bilayer WTe₂ in the absence of a magnetic field, providing a direct measure of the dipole moment of the Berry curvature.

Spectroscopic study of the low-energy excitations in magnetite Fe₃O₄ shows the signatures of its charge-ordered structure involved in the metal–insulator transition, whose building blocks are the three-site small polarons, termed trimerons.

Optoelectronic experiments show that a monolayer of WTe₂ is a material that simultaneously has topological electronic states and electron wavefunctions with a dipole in their Berry curvature.

Measuring the photocurrent response to circularly polarized mid-infrared light provides direct access to the chirality of Weyl fermions in Weyl semimetals — the property responsible for a range of exotic phenomena.

The emergent phenomena that characterize quantum materials have received prominent exposure thanks to experimental techniques based on photoemission. In turn, the challenges and opportunities presented by quantum materials have driven improvements in the photoemission technology itself.