Under high pressure, the thermoelectric material Mg 3 Bi 2 exhibits multiple phase transitions and two newly discovered crystal structures.

Although the electron correlation (U) within d-orbital perovskite Mott-systems is the root-cause for their unconventional functionalities, such as metal-to-insulator transitions (MIT), high-TC superconductivity, and multiferroics, it yet lacks strategy to modulate their U. Herein, we enable the tunability in U for correlated perovskite nickelates (RENiO3) by manipulating their RE-site covalency via introducing partial Bi-substitutions, based on which huge improvement in their electronic MIT abruptions beyond one order was achieved. The more covalent bonding between Bi-6s and O-2p enlarges the Ni-3d occupancy that enlarges U by 2-3 times, as indicated by synchrotron-based X-ray absorption spectroscopies and first principal calculations. Consequently, the ground-state band gap (Eg) and resistivity are effectively increased, giving rise to significant enhancement in their resistive switches across adjustable critical temperatures (TMIT) within 75-400 K, by up to 40 times. Simultaneously, the Bi-substitutions concurrently descend TMIT owing to their larger sizes than RE3+, indicating the prevailing dominance in the relative phase stability by the O-2p to Ni-3d charge transfer gap. This unravels the mystery in U that only electronically enlarges the ground-state Eg and resistivity rather than determines the relative phase stability across MIT (or TMIT). Tuning U via A-site covalency provides new freedom for optimizing functionalities of correlated perovskites.

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.

Layer-by-layer oxidation of a Ni(111) single crystal was performed to investigate the interface electronic states at the buried NiO/Ni interface. The transformation of nickel from its metallic to oxidized states was studied using in situ X-ray photoelectron spectroscopy and synchrotron radiation X-ray absorption spectroscopy after oxidation at high temperatures in an oxygen atmosphere. Multiple electronic surface states were detected during the initial oxidation stage when the NiO thickness was below one monolayer. The oxidation process involved the coupled migration of Ni atoms from the interior to the surface and the concurrent penetration of oxygen atoms from the exterior to the interior. The presence of metallic nickel on the surface after oxidation indicates that the partial decomposition of NiO occurs at high temperatures under ultrahigh vacuum conditions.

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.

The advent of fourth-generation synchrotron light sources has precipitated a surge in high-dimensional angle-resolved photoemission spectroscopy (ARPES) data, rendering manual extraction of band dispersions a primary bottleneck in electronic structure analysis. While deep-learning techniques offer automation, their “black-box” nature and heavy reliance on extensive labeled training datasets often limit their interpretability and applicability in data-sparse regimes. Here, we present a robust and scalable physics-informed framework based on Markov Random Field (MRF) for the automated reconstruction of electronic band structures. By bridging idealized density functional theory (DFT) priors with noisy experimental observations, our approach implements a multi-stage pipeline that ensures both physical consistency and computational efficiency. Key methodological innovations include: A dual-path calibration module that enables precise momentum alignment and automated energy-shift optimization via second-derivative landscapes, ensuring robust theory-experiment coupling. A k-d-tree-based regularization strategy that effectively mitigates experimental noise and eliminates boundary artifacts common in traditional image-processing workflows. We validate this framework on the Kagome metal RbTi3Bi5 and the Au(111). Our results demonstrate that the model successfully disentangles complex electronic features — including high-velocity Dirac cones, subtle type-II Dirac points, and flat bands — from congested spectra. Unlike purely data-driven models, this MRF-based inference engine provides high physical interpretability and remains effective in limited-data regimes. This verifiable pipeline establishes a foundation for high-throughput analysis and paves the way for autonomous “self-driving” ARPES experiments at next-generation light sources.

Correlated perovskites display extraordinary analog functionalities catering to neuromorphic computing and advanced field perceptions, transcending post-Moore limitations. Nevertheless, it is yet infeasible to achieve scalable material growth of correlated perovskites at micrometer-scale thicknesses, a prerequisite for enabling device resistances compatible with analog circuit requirements. Herein, we demonstrate ultra-effective growth of archetypal metastable correlated perovskites, e.g. nickelates (RENiO3), via liquid-phase epitaxy within alkali-chloride molten salts, realizing micrometer-scale thickness and scalability. The molten salts provide an ultra-stable thermodynamic environment and consistent ionic-precursor availability for long-period oriented growth, effectively enabling stacking faults formation to mitigate high-magnitude lattice mismatches. This bridges current technological gaps in micrometer-thick film growth of RENiO3 and achieves record-competitive electronic phase transitions at analog-compatible resistances, enabling more effective and energy-efficient analog cryogenic alarming applications. For the first time, wafer-scale RENiO3 with high uniformity was successfully grown within low-melting-point eutectic alkali chlorides, eliminating previous reliance on MPa-high oxygen pressures. Our strategy was extendable to multiple oxide systems, covering diverse functionalities, e.g. colossal magnetoresistance, oxide electrodes, and superconductivity.

Strongly correlated quantum states, such as charge density waves (CDWs), are exquisitely sensitive to Fermi surface topology and lattice symmetry, and are typically quenched by heavy carrier doping. In two-dimensional (2D) systems, however, macroscopic geometric curvature emerges as a novel structural degree of freedom to modulate microscopic quantum coherence. This raises a compelling physical question: can non-Euclidean geometric deformations compete with extreme electronic perturbations to reshape, or even revive, a quenched macroscopic quantum order? Here, by constructing monolayer TiSe_2-NbSe_2 heterostructure on a BLG/SiC substrate for the first time, we report the curvature-driven revival of a frustrated charge order in a non-Euclidean space. Low-temperature angle-resolved photoemission spectroscopy (ARPES) reveals a massive interfacial charge transfer, which destroys the global Fermi surface nesting and completely suppresses the long-range CDW order in Euclidean flat regions. Strikingly, high-resolution scanning tunneling microscopy (STM) reveals that a novel, non-linear CDW state miraculously survives, remaining strictly localized within morphologically distorted, non-Euclidean nanoscale curved regions. Atomistic simulations unravel the structural origin of this phenomenon, demonstrating that interfacial twist and lattice mismatch spontaneously generate a corrugated superlattice.

The thermoelectric materials Mg3Bi2 and related compounds exhibit a high figure of merit (zT) combined with attractive properties for commercialization, such as low cost, elemental abundance, non-toxicity, and good processability. These advantages make them highly promising candidates for developing high-performance flexible thermoelectric devices. While previous research has primarily focused on improving thermoelectric properties through chemical doping, the effects of pressure on the crystal structure and corresponding thermoelectric properties have not been fully investigated. In this study, we combined first-principles calculations, crystal structure prediction, and X-ray absorption near-edge structure (XANES) measurements to probe the behaviour of this material under extreme conditions. Our investigation revealed a low-lying P21/m structure at 5 GPa, competitive in energy with the known C2/m phase, and two novel high-pressure phases: a Pnnm structure at 30 GPa and a P21/c structure above 80 GPa. To understand the pressure-induced structural evolution, we systematically evaluated the energy stability, dynamical stability, and thermoelectric properties of each phase.

The organic–inorganic hybrid (BEDT-TTF)3[Cu2(μ-C2O4)3·CH3CH2OH·1.2H2O] (I) was obtained using the electrocrystallization method. It comprises a θ21-phase organic donor layer and a two-dimensional inorganic antiferromagnetic honeycomb lattice. Cu(II) is octahedrally coordinated by three bisbidenetate oxalates, exhibiting Jahn–Teller distortion. CH3CH2OH and H2O molecules are located within the cavities of the honeycomb lattice. The total formal charge of the three donor molecules was assigned to be +2 based on the bond lengths in the TTF core, which corresponded to the Raman spectra. It is a semiconductor with σrt = 0.04 S/cm and Eα = 40 meV. No long-range ordering was observed above 2 K from zero-field cooling/field cooling magnetization, as confirmed by specific heat measurements. The spin frustration with f > 10 from the antiferromagnetic copper-oxalate-framework was observed. It is a candidate quantum spin liquid.

The quantum anomalous Hall (QAH) effect in two-dimensional (2D) topological materials has attracted widespread attention due to its potential for dissipationless chiral edge transport without an external magnetic field, which is highly promising for low-power electronic applications. However, identifying materials that exhibit these properties remains particularly challenging, as only a limited number of such materials are known, raising the intriguing question of whether it is possible to induce the QAH effect in materials with ordinary properties through structural modifications. In this work, we grow an unreported 2D titanium selenide (Ti3Se4) on a Cu(111) substrate using molecular beam epitaxy. Low-energy electron diffraction and scanning tunneling microscopy characterizations reveal a 7×7 brick-like structure. First-principles calculations and X-ray photoelectron spectroscopy measurements confirm its composition to be Ti3Se4. Our calculations further demonstrate that monolayer Ti3Se4, in its grown form on Cu(111), has the potential to host the QAH effect. Interestingly, when we examine its freestanding form, the monolayer transitions from a QAH insulator candidate into a conventional semiconductor, despite only minor differences in their atomic structures. This transition enlightens us that subtle lattice adjustments can induce a transition from semiconductor to QAH properties in freestanding Ti3Se4. This discovery provides a potential route to engineering practical materials that may exhibit the QAH effect.

HfO2-based thin films possess the merits of robust ferroelectricity at the nanoscale and compatibility with modern Si technology, show great potential in nanoelectronics. However, the high coercive field (Ec) of such fluorite-structure oxide ferroelectrics usually leads to undesired endurance performance and dielectric breakdown, which impedes their practical applications. Herein, the Ho-doped HfO2 (HHO) film with high polarization and superior ferroelectric endurance is reported, enabled by local structural engineering through holmium doping and thickness modulation. The predominantly (111)-oriented films display enhanced remanent polarization (35 µC cm-2) and excellent endurance without failure even after 1011 electric field cycles. The evolved rhombohedral distortion and stronger chemical bonding, regulated by local structure engineering, can avoid defect aggregation to overcome the undesirable fatigue drawback in the ferroelectric phase (Pca21). These results are significant in stabilizing ferroelectric hafnia-based films and make them more suitable for long-lasting device applications.

Altermagnets constitute an emerging class of collinear magnets that exhibit zero net magnetization yet host spin-split electronic bands arising from non-relativistic spin-space-group symmetries. Realization of altermagnetism in the two-dimensional (2D) limit remains an outstanding challenge because dimensional reduction suppresses kZ dispersion and destabilizes the symmetry operations essential for spin compensation. Here, we investigate ultrathin CrSb films grown epitaxially on Bi2Te3 substrate and uncover the evolution of altermagnetism in the 2D limit. Scanning tunneling microscopy (STM), quasiparticle interference (QPI), angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT) calculations show that interfacial symmetry breaking in the one-unit-cell (1 UC) limit gives rise to localized electronic states and uncompensated magnetic moments. These interfacial effects become weakened from 7/4 UC, accompanied by the recovery of a bulk-like coordination environment and the emergence of altermagnetic electronic characteristics. Our results show that the essential altermagnetic electronic structure of CrSb survives at a thickness of only 1.05 nm, demonstrating the robustness of altermagnetism in the 2D limit and opening opportunities for integrating stray-field-free spin order into low dimensional spintronic architectures.

As a fundamental structural feature, the symmetry of materials determines the exotic quantum properties in transition metal dichalcogenides (TMDs) with charge density waves (CDWs). The Janus structure, an artificially constructed lattice, provides an opportunity to tune the electronic structures and their associated behavior, such as CDW states. However, limited by the difficulties in atomic-level fabrication and material stability, the experimental visualization of the CDW states in two-dimensional (2D) TMDs with Janus structure is still rare. Here, using surface selenization of VTe2, we fabricated monolayer Janus VTeSe. With scanning tunneling microscopy, we observed and characterized an unusual [Formula: see text] CDW state with threefold rotational symmetry breaking. Combined with theoretical calculations, we find that this CDW state can be attributed to the magnetic-involved charge modulation in the Janus VTeSe, rather than the conventional electron-phonon coupling. Our findings provide a promising platform for studying the CDW states and artificially tuning the electronic properties of the 2D TMDs toward the related fundamental and applied studies.

The graphitic carbon nitride (g-C3N4) is an important optoelectronic and photocatalytic material; however, its application is limited by the high recombination rate of the electron-hole (e(-)-h(+)) pairs. In this work, we reported a novel strategy combining two-step annealing treatment and ionic-liquid (IL) gating technology for effectively regulating the properties of g-C3N4, especially largely reducing the recombination rate of the e(-)-h(+) pairs, which is evidenced by a remarkable reduction of the photoluminescence (PL) intensity. Firstly, g-C3N4 samples with typical layered structure were obtained by annealing melamine with temperature of 600 degrees C. Further annealing of the samples at 600 degrees C with much longer time (from 4 h to 12 h) were found to effectively reduce the imperfections or defects, and thus the PL intensity (49% reduction). This large reduction of PL intensity is attributed to the improved interconnection of triazine units, the shortened charge transfer diffusion distances, and the reduced interlayer spacing, which facilitate electron relocation on the g-C3N4 surface. Secondly, by post-treating the annealed sample with IL, the PL intensities were found to be further reduced, mainly due to the passivation of charged defect centers by IL. Additionally, applying an external electric field in an IL environment can significantly enhance the charged defect passivation. Overall, by utilizing electric field-controlled IL gating, defect states in g-C3N4 were passivated, leading to a significant reduction in PL intensity and an extension of PL lifetime, thereby effectively decreasing the e(-)-h(+) recombination rate in the material. This study demonstrates a new approach for defect passivation, providing insights and strategies for modulating properties of advanced materials such as g-C3N4.

The anion-deficient layered perovskite Pb2Fe2O5, featuring a polarizable active Pb cation with lone pair electrons and a magnetically active transition metal Fe cation, presents a promising candidate for multiferroic applications. Nonetheless, the exploration of multiferroic properties and magnetoelectric coupling in Pb2Fe2O5 is extremely rare due to its complex structure. Herein, a colossal magnetoelectric coupling coefficient (5.19 × 105 mV cm-1 Oe-1), high ferroelectric polarization (2 μC/cm2), and magnetic moment (25 emu/cc) at room temperature have been discovered in an epitaxial Pb2+0.48Fe2O5 film. The findings of this study demonstrate that the introduction of excessive Pb ions can disrupt the disordered arrangement of the mixed layer and convert it to an ordered distribution to improve ferroelectric properties. This research not only enriches the magnetoelectric coupling material system but also offers a viable strategy for achieving strong room-temperature magnetoelectric coupling and multiferroicity in layered oxide materials.

Ferromagnetic insulators are receiving ever-increasing research activities driven not only by the unique advantage of low power loss during spin-wave-based information processing but also by the potential to construct next-generation spintronic devices. However, either the exceedingly rare candidates or the low Curie temperature far below room temperature greatly hinder their practical application. Here, through the modulation of a novel three-dimensional (3D) tensile strain, a room-temperature ferromagnetic insulating state with a Curie temperature as high as 594 K is achieved in self-assembled LaCoO3 & ratio;MgO nanocomposite thin films. Atomically resolved electron microscopy quantifications identify the 3D strain state of the thin film, where the +2.6% out-of-plane and +2.1% in-plane tensile strains are attributed to the interphase mismatch between the LaCoO3 and MgO building blocks and epitaxial constraint, respectively. Combined with the assessment of electronic states and theoretical analysis, we correlate the strain state with the resulting ferromagnetic insulating property and clarify the underlying mechanisms, by which the emergent strain states break the degeneracy of crystal-field splitting and tailor the on-site Coulomb interactions and spin configuration. These findings underscore the efficacy of a three-dimensional strain strategy in engineering the long-desired high-temperature ferromagnetic insulators via the manipulation of strong spin-lattice coupling, providing a promising approach for the exploitation of exotic functionalities in correlated oxides.

Owning various and unique properties, the crystalline phases of transition metal dichalcogenides (TMDs) and the introduced phase engineering have a range of potential applications in future devices. The phase transition temperature, corresponding to the stability of the atomic structural phase, is one of the key parameters in the phase engineering study. However, the reported method for tuning the transition temperature is always complicated and brings impurities, impairing the properties. Here, tuning the phase transition temperature via the surface oxidation of the octahedral phase (1T)-TaS2 is reported. The surface characterization results reveal that the phase transition would originate from the sulfur surface sublimation and its induced doping. Then the Ta oxide layer, a surface cap, is fabricated using O2 plasma treatment, without affecting the 1T-TaS2 under the surface. As revealed by the Raman results, the phase transition temperature of 1T-TaS2 increase significantly, in contrast to the samples without oxidation. The work provides a facile and effective method to tune the phase of the TMDs, toward the fabrication of the nanostructure based on the phase engineering for future applications.

Three key aspects of magnetic topological materials, i.e., band topology, magnetic order and anomalous transport are closed related with each other, laying the ground for exotic phenomena such as topological magnetoelectric and magneto-optical effects. Here in the ferromagnetic Weyl semimetal PrAlSi, we report negligible effect of magnetic order on the band structure featuring Weyl fermions, as directly observed by angle-resolved photoemission spectroscopy. Instead, both anomalous and normal Hall effects show clear temperature/magnetism dependence. While the longitudinal conductivity ( σ_xx ) is deep in the empirically intrinsic region, the anomalous Hall conductivity ( σ_AHE ) is quadratically proportional to σ_xx , suggesting giant anomalous Hall angle at moderate σ_xx . Our findings point to disentangled band topology and anomalous transport, as well as the possibility to achieve high σ_AHE in highly conductive, ultrathin PrAlSi, suitable for anomalous Hall sensors and spin-transfer torque application. Magnetic topological materials exhibit intertwined band topology, magnetic order, and anomalous transport, leading to unique phenomena. Here, the authors study the ferromagnetic Weyl semimetal PrAlSi, revealing negligible magnetic order effects on Weyl fermions but significant temperature-dependent Hall effects, including a giant anomalous Hall angle, suggesting potential for high-performance anomalous Hall sensors and spin-transfer torque applications.