Skyrmions in 2D magnets are promising candidates for nonvolatile, low-power, and high-density spintronic memories. However, their experimental realization at the 2D limit remains challenging, owing to the difficulty in engineering the required chiral magnetic interactions. Here, we report the creation and direct imaging of Néel-type skyrmions in Janus 2D chromium chalcogenides using synchrotron X-ray photoemission electron microscopy, and scanning nitrogen-vacancy magnetometry, which exhibit field-free stability, nonvolatility, and size tunability. First-principles calculations and micromagnetic simulations reveal that Janus-surface-induced inversion-symmetry breaking enhances the Dzyaloshinskii-Moriya interaction, providing the microscopic mechanism for skyrmion stabilization and tunability. We further achieve reversible skyrmion writing and erasing using a single ultrafast laser pulse in a magnetic field as low as 300 Oe, demonstrating the excellent manipulability of this 2D magnetic system. These results establish Janus engineering as a route to creating and manipulating nonvolatile skyrmions in atomically thin magnets, with implications for skyrmion-based low-power spintronic devices.

ABSTRACT Berry curvature in transition metal dichalcogenides (TMDs) critically governs spin‐valley degrees of freedom, nonlinear/quantum electrical transport, and magnetoelectric coupling, underpinning emergent functionalities in valleytronic, magnetoelectric, and optoelectronic devices. Self‐intercalated Cr 1+ δ Te 2 , as a representative magnetic semimetal among TMDs, enables controlled the Berry curvature due to its rigid band shift under external stimuli. In this work, we study the thickness‐tuned Berry curvature, manifested by intrinsic anomalous Hall effect (AHE), in van der Waals (vdW) epitaxial Cr 3 Te 4 ( δ = 0.5) ultrathin films. At low temperatures, the intrinsic AHE of Cr 3 Te 4 ultrathin film has a negative‐polarity below 13 monolayers and positive‐polarity for 22 monolayers. This sign reversal, indicating the Berry curvature modulation, could be attributed to the Fermi level shift caused by Te(CrTe 2 )‐termination at the surface and interface. These findings highlight the crucial role of controlling the electronic structure of vdW materials at atomic scale and pave the way for the design of high‐density, miniaturized topological spintronic devices.

Surface plasmons (SPs) in refractory materials like titanium nitride (TiN) offer promising alternatives to noble metals for plasmonic applications due to their robustness and CMOS compatibility. However, the dispersion behavior of SPs at the surface of TiN in the non-retarded regime remains poorly understood. Here, we employ momentum-resolved high-resolution electron energy loss spectroscopy to investigate the collective electronic excitations of atomically flat TiN(111) thin films treated by Ar+ sputtering and annealing. Two distinct excitations are observed: a SP mode near 2 eV and a defect-induced interband transition (IT) mode around 1 eV. The SP exhibits an anisotropic, anomalous dispersion: negative at small momenta (q < 0.03 & Aring;(-1) along Gamma M & strns; and q < 0.025 & Aring;(-1) along Gamma K & strns; ), transitioning to positive at larger momenta. The spectral weight of the IT shows an opposite momentum dependence to the SP energy. Assisted by a Drude-Lorentz dielectric model incorporating the momentum-dependent IT oscillator strength, we demonstrate that the anomalous SP dispersion arises from q-dependent screening by defect states. These findings highlight defect engineering as a strategy for tailoring plasmonic properties in refractory nitrides, with implications for integrated photonics and sensing applications.

Excitonic band structure is critical for investigating exciton dynamics. Theoretically, quantum effects from exchange scattering between electron-hole pairs significantly modulate exciton dispersion. Here, we report the direct observation of dimensionality-dependent exciton dispersion in a single-band Mott insulator Nb3Cl8 through high-resolution electron energy loss spectroscopy. In the high-temperature phase, the exciton in Nb3Cl8 hosts an exceptionally large binding energy, and exhibits clear quasi-two-dimensional massless linear dispersion. In contrast, in the low-temperature phase, the exciton splits into two bands, both displaying three-dimensional parabolic dispersion. These dramatic changes in the exciton dispersion stem from the dimensional mutation driven by a substantial enhancement of interlayer coupling across the phase transition. This Letter provides a clear and typical example of how exciton behavior evolves with dimensionality.

Orbital order describes a quantum state where occupied orbitals line up in a periodic pattern. While orbital physics plays a fundamental and universal role in strongly correlated electron systems, the existence and particularly the band structure fingerprint of orbital order remain a long-standing mystery. Here, we report the discovery of rare earth 5d-orbital order developed by the surface states of intermetallic compound Tb2CoAl4Ge2. Angle-resolved photoemission spectroscopy reveals characteristic nematic features like Fermi surface deformation and band split. These experimental observations can be described by a ferro-orbital order term in the mean-field Hamiltonian. The structural and magnetic origin of such order is excluded by systematic high-resolution neutron powder diffraction and scanning tunnelling microscopy measurements. Our results provide strong evidence for a pure surface orbital order scenario avoiding complications from structural distortion as in colossal magnetoresistance manganites, magnetic order as in iron-based superconductors, and charge transfer p-orbital order in cuprates.

We report nonreciprocal charge transport in epitaxial monoclinic SrIrO3 (m-SIO) thin films, a nonsymmorphic symmetry-protected Dirac semimetal with strong spin-orbit coupling. Second-harmonic magnetotransport measurements reveal both bilinear magnetoelectric resistance and a nonlinear planar Hall effect, providing clear evidence of spin-momentum locked states in m-SIO. Systematic angular-dependent measurements suggest a predominantly in-plane spin vector oriented perpendicular to the electron momentum, consistent with Rashba-type spin-momentum locking on the Fermi surface. Quantitative analysis of the bilinear magnetoelectric resistance based on a simplified Rashba model yields a large effective Rashba parameter, suggesting that the Rashba-type surface states are closely related to the strongly spin-orbit coupled electronic structure of the nonsymmorphic Dirac bulk states. Our results provide a transport route to probe Rashba-type spin-momentum locking in m-SIO and identify m-SIO as a promising platform for oxide spin-orbitronics.

The pyrochlore iridates RIrOhave emerged as a unique playground for exploring exotic quantum phenomena arising from the intricate interplay of strong spin-orbit coupling, electron correlations, and geometric frustration. While bulk crystals of these materials have revealed a rich landscape of correlated and topological states, recent breakthroughs in epitaxial thin-film synthesis and heterostructure engineering unlocked an entirely new dimension of discovery. This brief Perspective reviews recent advancements highlighting how new tuning knobs such as dimensional confinement, epitaxial strain, and interfacial coupling can be used to manipulate the delicate balance of competing interactions. We discuss several key discoveries enabled by this approach including the realization of the magnetic Weyl semimetal phase in (111) oriented films, strain-engineered magnetic multipolar orders, the emergence of a chiral spin liquid-like state in the quasi-2D limit, and the discovery of novel electronically anisotropic states at interfaces between pyrochlore iridates and other quantum materials, such as spin ice pyrochlores. These findings showcase that low-dimensional pyrochlore iridates provide ample opportunities for both theory and experiment to unravel, control and ultimately design novel quantum states of matter. We conclude by outlining key open questions and future directions ranging from the synthesis of new heterostructures to the application of advanced probes and the exploration of non-equilibrium phenomena.

We investigate the electron band structure of grey arsenic, whose (111) face hosts the topological Shockley state. Interestingly, the bulk band close to the touching point with the surface state exhibits the characteristics of inelastic scattering. Moreover, the band structure analysis reveals linearity in the imaginary part of electron self-energy. These features are analogous to those observed in high-temperature superconductors and marginal Fermi liquid systems, respectively, where strong electronic correlations exist. Our results suggest that correlated many-body states can be connected by non-interacting topological states, providing a viable playground to explore the coupling between topological and correlated states via grey arsenic surface.

Two-dimensional (2D) semiconductor Bi2O2Se has emerged as a promising channel material in post-Moore transistors. To realize its potential for industrial applications, a facile and reliable synthesis method for large-area, uniform, single-crystalline Bi2O2Se films on industrially compatible substrates is highly desired. However, existing approaches typically rely on solid-source evaporation, which suffers from poor precursor volatility and irreproducible mass transfer. Moreover, the epitaxial growth of 2D Bi2O2Se has been predominantly confined to non-scalable substrates such as perovskite oxides or mica. Here we report a metal-organic chemical vapor deposition (MOCVD) route to high-quality, single-crystalline Bi2O2Se films grown directly on industrially compatible r-plane sapphire. By employing triphenylbismuth and elemental selenium as volatile precursors, we achieve uniform and reproducible 2D film growth. Field-effect transistors fabricated from these films exhibit outstanding electrical performance, with an on/off ratio exceeding 105, and the highest mobility of ∼228 cm2 V−1 s−1.

Orbital order describes a quantum state where occupied orbitals line up in a periodic pattern. Although orbital physics plays a fundamental and universal role in strongly correlated electron systems, the existence and particularly the band-structure fingerprint of orbital order remain a long-standing mystery. Here we report the discovery of rare earth 5d-orbital order developed by the surface states of the intermetallic compound Tb2CoAl4Ge2. Angle-resolved photoemission spectroscopy reveals characteristic nematic features such as Fermi surface deformation and band splitting. These experimental observations can be described by a ferro-orbital order term in the mean-field Hamiltonian. The structural and magnetic origin of such order is excluded by systematic high-resolution neutron powder diffraction and scanning tunnelling microscopy measurements. Our results provide strong evidence for a pure surface orbital order scenario avoiding complications from structural distortion as in colossal magnetoresistance manganites, magnetic order as in iron-based superconductors and charge transfer p-orbital order in cuprates.

Crystal structure engineering is pivotal for tailoring material properties, particularly in atomically thin two-dimensional (2D) transition-metal chalcogenides that exhibit rich, crystal-phase-dependent electronic, optical, and magnetic properties. However, their crystal-phase-controlled synthesis remains a critical challenge that limits their practical applications. Here, we report the phase-controlled synthesis of atomically thin chromium telluride films, including CrTe3, CrTe2, Cr1+δTe2, and CrTe, on graphene/SiC substrates via precise tuning of molecular beam epitaxy parameters. The growth mechanism is further revealed. We have systematically characterized the different structures and electronic, chemical, and magnetic properties of these films using scanning tunneling microscopy/spectroscopy, scanning transmission electron microscopy, density functional theory calculations, X-ray photoelectron/absorption spectroscopy, and circular-polarized X-ray photoemission electron microscopy. Heterostructures of different chromium telluride phases are further fabricated, demonstrating band engineering enabled by phase control of chromium tellurides.

Electron-boson coupling is central to a comprehensive understanding of the diverse physical phenomena emerging from many-body interactions. Yet less attention has been paid to how plasmons, collective bosonic modes of electron density oscillation, interact with conduction electrons and how external parameters can tune this interaction. Here, we present a clear display of composite quasiparticles stemming from electron-plasmon coupling, known as the plasmonic polaron, in self-intercalated 1T-TiS2, by using angle-resolved photoemission spectroscopy (ARPES), high-resolution electron energy loss spectroscopy (HR-EELS) and first-principles calculations. The single particle spectral function exhibits a distinctive plasmon-loss satellite with the same characteristic energy scale determined by HR-EELS measurements. The bosonic energy scale of plasmonic polaron is tunable by controlling charge carrier density and temperature, distinguishing itself from conventional polarons arising from electron-phonon interactions. Furthermore, we find that the dielectric screening strongly affects the formation of the plasmonic polaron states. Our findings provide direct spectroscopic evidence of plasmonic polarons and establish self-intercalated layered materials as a promising platform for studying, controlling, and harnessing plasmonic interactions in quantum materials.

SrRuO3 is a canonical itinerant ferromagnet, yet its properties in the extreme two-dimensional limit on a (111) crystal plane remain largely unexplored. Here, we demonstrate a complete transformation of its ground state driven by dimensional reduction. As the thickness of (111)-oriented SrRuO3 films is reduced to a few unit cells, the system transitions from a metallic ferromagnet to a semiconducting antiferromagnet. This emergent antiferromagnetism is evidenced by a vanishing magnetic remanence and most strikingly, by the appearance of an unconventional twelve-fold anisotropic magnetoresistance. First-principles calculations confirm that an A-type antiferromagnetic order is the stable ground state in the ultrathin limit. Our findings establish (111) dimensional engineering as a powerful route to manipulate correlated electron states and uncover novel functionalities for antiferromagnetic spintronics.

Metal-organic framework (MOF) materials exhibit great potential in the field of electrocatalysis due to their high specific surface area, tunable pore structures, and abundant active sites. However, further enhancement of their electrocatalytic performance is often limited by factors such as electron transport efficiency, accessibility of active sites, and interfacial reaction kinetics. Interface engineering strategies have been proposed as a promising strategy for modifying MOF-based catalysts for optimizing their catalytic performance. Significant progress has been made in recent years. Based on this, this review summarizes recent developments in interface modification to enhance MOF materials, focusing on the unique effects induced by the interfacial modification of MOF materials, such as optimizing electron transport and conductivity, increasing the exposure of active sites, improving mass transfer of reactants/products, and stabilizing interfacial structures. Additionally, the applications of various types of MOF-based composite materials for promoting electrocatalytic performance that induced by interfacial effects are also manifested. Finally, the challenges and perspectives of this interesting field are also discussed to offer guidance for the future design of more advanced MOF-based electrocatalysts.

We introduce a rapid, accurate framework for computing atomic migration barriers in crystals by combining universal machine learning force fields (MLFFs) with 3D potential energy surface sampling and interpolation. Our method suppresses periodic self interactions via supercell expansion, builds a continuous PES from MLFF energies on a spatial grid, and extracts minimum energy pathways without predefined NEB images. Across twelve benchmark electrode and electrolyte materials including LiCoO2, LiFePO4, and LGPS our MLFF-derived barriers lie within tens of meV of DFT and experiment, while achieving 10^2 x speedups over DFT-NEB. We benchmark GPTFF, CHGNet, and MACE, show that fine-tuning on PBE/PBE+U data further enhances accuracy, and provide an open-source package for high-throughput materials screening and interactive PES visualization.

Nonadiabatic effects profoundly influence lattice dynamics, resulting in phonon renormalizations not only at the center of Brillouin zone (BZ), but also across the entire dispersion at finite momenta. These nonadiabatic phenomena exhibit clear dimensional dependencies and remain largely unexplored experto investigate nonadiabatic phonon dispersion renormalization in monolayer graphene (MLG) and Bernal bilayer graphene (BLG). We present comprehensive phonon spectra measurements for both MLG and BLG across the full BZ. The high-resolution data reveal an intriguing "W" -shaped dispersion for the longitudinal optical phonon in MLG and a "V" -shaped dispersion in BLG near the BZ center, in contrast to the conventional "U" -shaped parabolic dispersions. Combining theoretical analysis, these anomalous phonon renormalizations are demonstrated to originate from nonadiabatic electron-phonon couplings. The comparative study of MLG and BLG gives a generic understanding of the impact of nonadiabatic effects on phonon dispersions in doped two-dimensional systems.

Perovskite ruthenates are fascinating playgrounds for exploring topological spin textures but generally rely on extrinsic mechanisms to trigger the noncoplanar states. Here, we report the discovery of an emergent chiral spin crystal phase in (111) SrRuO3 epitaxial films, characterized by a significant topological Hall effect and noncoplanar spin arrangements with different propagation vectors along two orthogonal directions. Instead of being driven by the enhanced Dzyaloshinskii-Moriya interaction due to broken inversion symmetry at heterointerfaces, this emergent state arises intrinsically from the interplay of dipolar interactions and magnetic frustration, leading to the stabilization of topological phases in much thicker films. These findings highlight a potential route for creating and controlling the topological spin states in perovskites with broad implications for spintronic device design.