Discovery of an intermediate nematic state in a bilayer kagome metal ScV6Sn6

Nature Communications · 2025-08-23 · 4 citations

Abstract Nematicity, spontaneous breaking of rotational symmetry, is a ubiquitous phenomenon in correlated quantum matter. Here we show a phase transition in high-quality ScV 6 Sn 6 bilayer kagome metal at a temperature $${T}^{*}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msup> </mml:math> , occurring seven Kelvins below the charge density wave transition at $${T}_{{CDW}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>C</mml:mi> <mml:mi>D</mml:mi> <mml:mi>W</mml:mi> </mml:mrow> </mml:msub> </mml:math> , as indicated by thermodynamic, transport, and optical measurements. This emerging intermediate phase does not exhibit spontaneous time-reversal-symmetry breaking, as evidenced by zero-field Sagnac interferometry. However, it displays a strong, spontaneous in-plane anisotropy between $${T}^{*}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msup> </mml:math> and $${T}_{{CDW}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>C</mml:mi> <mml:mi>D</mml:mi> <mml:mi>W</mml:mi> </mml:mrow> </mml:msub> </mml:math> , revealed by transport and optical polarization rotation measurements. A pronounced depolarization effect detected by the Sagnac interferometer further confirms its nematic nature. Unlike AV 3 Sb 5 , this phase, alongside the recently discovered intra-unit cell nematic order at lower temperatures, presents a diverse landscape of nematicities at multiple length and temperature scales. Our findings highlight ScV 6 Sn 6 as a prime candidate for realizing symmetry-breaking phases driven by charge density competition, kagome physics, and Van Hove singularities.

Elucidating Relay Catalysis on Copper Clusters With Satellite Single Atoms for Enhanced Urea Electrosynthesis

Angewandte Chemie International Edition · 2025-03-10 · 31 citations

Abstract Relay catalysis represents significant efficacy in alleviating competition among different reactants during coupling reactions. However, a comprehensive understanding of the reaction mechanism underlying relay catalysis for the urea electrosynthesis remains challenging. Herein, we have developed a catalyst (Cu AC ‐Cu SA @NC) comprising Cu atomic clusters (Cu AC ) with satellite Cu─N 4 single atoms (Cu SA ) sites on the nitrogen‐doped porous interconnected carbon skeleton (NC), enabling elucidation of a relay catalysis process for co‐reduction of CO 2 and NO 3 − . The designed Cu AC ‐Cu SA @NC catalyst exhibits an approximately threefold higher urea yield rate compared to that of Cu SA @NC at −1.3 V versus RHE. Ex‐situ experimental results and in‐situ attenuated total reflection surface‐enhanced infrared absorption spectroscopy analysis reveal a formation sequence between the *NH 2 and *NH 2 CO species on Cu AC ‐Cu SA @NC with increasing reduction potential. The combination of theoretical calculations further elucidates that the relay catalysis pathway involves “Cu AC ” sites facilitating the conversion of *NO 3 to *NO x , followed by a hydrogenation process to form *NH 2 with *H from water dissociation promoted by “Cu SA ” sites, which subsequently couples with *CO 2 to produce urea. This work provides novel insights into the investigation of coupling reactions, but not limit to, urea synthesis.

Elucidating Relay Catalysis on Copper Clusters With Satellite Single Atoms for Enhanced Urea Electrosynthesis

Angewandte Chemie · 2025-03-10 · 3 citations

Abstract Relay catalysis represents significant efficacy in alleviating competition among different reactants during coupling reactions. However, a comprehensive understanding of the reaction mechanism underlying relay catalysis for the urea electrosynthesis remains challenging. Herein, we have developed a catalyst (Cu AC ‐Cu SA @NC) comprising Cu atomic clusters (Cu AC ) with satellite Cu─N 4 single atoms (Cu SA ) sites on the nitrogen‐doped porous interconnected carbon skeleton (NC), enabling elucidation of a relay catalysis process for co‐reduction of CO 2 and NO 3 − . The designed Cu AC ‐Cu SA @NC catalyst exhibits an approximately threefold higher urea yield rate compared to that of Cu SA @NC at −1.3 V versus RHE. Ex‐situ experimental results and in‐situ attenuated total reflection surface‐enhanced infrared absorption spectroscopy analysis reveal a formation sequence between the *NH 2 and *NH 2 CO species on Cu AC ‐Cu SA @NC with increasing reduction potential. The combination of theoretical calculations further elucidates that the relay catalysis pathway involves “Cu AC ” sites facilitating the conversion of *NO 3 to *NO x , followed by a hydrogenation process to form *NH 2 with *H from water dissociation promoted by “Cu SA ” sites, which subsequently couples with *CO 2 to produce urea. This work provides novel insights into the investigation of coupling reactions, but not limit to, urea synthesis.

Temperature-invariant magneto-optical Kerr effect in a noncollinear antiferromagnet

ArXiv.org · 2025-10-22 · 1 citations

The anomalous Hall effect and magneto-optical Kerr effect have traditionally been associated with ferromagnets, but recent studies reveal their presence in noncollinear antiferromagnets due to nonzero Berry curvature despite negligible net magnetization. However, Hall measurements often show strong temperature dependence caused by extrinsic scattering, complicating quantitative analysis, and temperature invariance of the Kerr effect remains unconfirmed. Here we employ epitaxial, stoichiometric Mn3NiN single crystal films and perform polar Kerr measurements at an infrared 1550 nm telecommunication wavelength, demonstrating a spontaneous Kerr signal that remains stable within a few percent across a 200 Kelvin range below the Néel temperature. This temperature-invariant Kerr effect contrasts with the strongly temperature-dependent Hall effect and confirms the intrinsic nature of Berry curvature in these materials. Our findings establish infrared Kerr effect as a reliable, local probe of Berry curvature in noncollinear antiferromagnets, facilitating quantitative characterization and advancing antiferromagnetic spintronic applications.

Ultra-thin surface chemical bonded polyanionic group for 4.7 V LiCoO2

Energy storage materials · 2025-06-06 · 1 citations

In Situ Observation of Redox Dynamics and Surface Restructuring on Pt/CeO2 Catalysts

Crystals · 2025-02-24

Heterogeneous catalysis has significant applications in energy conversion, chemical production, and environmental treatment. Among them, the supported catalyst Pt/CeO2 has attracted much attention due to its high catalytic activity and stability. While the particle size of the catalyst strongly influences its performance, the dynamic behavior and the underlying mechanism of the particle size effect under realistic reactions have not been fully clarified. Using in situ transmission electron microscopy and mass spectrometry, we systematically investigated the size-dependent surface restructuring of Pt nanoparticles supported on CeO2 in high-temperature redox environments. Larger Pt nanoparticles exhibited significant surface fluctuations during oxidation, which could be reconstructed under reducing conditions, with a slight rotation after the reaction cycle. In contrast, smaller Pt particles demonstrated greater stability, maintaining a constant size after the reaction while their surface structures continuously restructured into low-index crystal planes during oxidation. Mass spectrometry revealed water production during the catalytic process, highlighting a correlation between surface restructuring and reactivity. These findings advance the understanding of redox dynamics in noble metal catalysts and provide a theoretical basis for the design of more efficient and stable catalytic systems.

Resolving the discrepancy between MOKE measurements at 1550-nm wavelength on kagome metal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Cs</mml:mi><mml:msub><mml:mi mathvariant="normal">V</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>Sb</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:mrow></mml:math>

Physical Review Materials · 2024-01-12 · 11 citations

Kagome metals $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ ($A=\mathrm{K}$, Cs, Rb) provide a rich platform for intertwined orders such as the charge density wave (CDW) and a chiral order with time-reversal symmetry breaking (TRSB). While early reports of large optical polarization rotations have been interpreted as the magneto-optic Kerr effect (MOKE) and as evidence for TRSB, recent dedicated optical rotation and MOKE experiments have clarified that this large optical rotation originates instead from an unconventional specular rotation. Yet a critical discrepancy remains regarding the possible existence of a true spontaneous MOKE signal: in experiments performed after training with modest magnetic fields of up to 0.3 T, no MOKE signal was detected above the noise floor of 30 nanoradians, while microradian-level signals were found in an experiment using higher training fields. This raises an intriguing possibility of different zero-field ground states with opposite time-reversal symmetry properties, because of different magnetic histories. To unambiguously determine whether a training-field-dependent spontaneous MOKE signal exists in $\mathrm{Cs}{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$, we conduct comprehensive MOKE measurements with two Sagnac interferometer setups capable of both low and high training fields of up to 9 T, and perform careful analyses of contributions of signals from various optical components. We conclude that there is no observable spontaneous MOKE signal, hence no optical evidence for TRSB, regardless of the magnitude of training fields and the speed of temperature ramping.

Atomically Resolved Surface Reconstruction of WO₃ (002)

Small · 2024-11-08 · 3 citations

Abstract The rearrangement of surface atoms in oxide nanocrystals, namely surface reconstruction, plays an important role in improving the physical and chemical properties of metal oxides. However, structural information pertaining to reconstructed surfaces is scarce due to the challenges associated with directly imaging surface and sub‐surface atoms under reconstruction conditions. Herein, the reconstruction of the nanocrystalline tungsten trioxide (002) surface is directly investigated via scanning transmission electron microscope (STEM). The results reveal that the atoms on the reconstructed WO 3 (002) surface are rearranged into a (1 × 2) structure, and the structural model is determined by density functional theory (DFT) calculation. In addition, after surface reconstruction, the Fermi level shifted toward the conduction band compared to the initial surface, achieving an effect similar to n‐type doping. Surprisingly, analogous atomic rearrangements are also observed in cracks, indicating that sub‐nanometer fractures in tungsten trioxide can be remedied through surface reconstruction, thus proposing an unconventional mechanism for crack healing. Furthermore, DFT calculations are used to analyze the models and electronic properties of the reconstruction structures. These findings provide insights into the surface reconstruction of WO 3 (002) and the healing of nanoscale cracks in tungsten trioxide.

Atomic-scale imaging of structural evolution from anatase TiO2 to cubic TiO under electron beam irradiation

Nano Today · 2024-10-30 · 11 citations

Robust Ferroelectricity in Nonstoichiometric 2D AgCr_1‐xS₂ via Chemical Vapor Deposition

Small · 2024-12-15 · 3 citations

Abstract Ferroelectricity in two‐dimensional (2D) materials at room temperature has attracted significant interest due to their substantial potential for applications in non‐volatile memory, nanoelectronics, and optoelectronics. The intrinsic tendency of 2D materials toward nonstoichiometry results in atomic configurations that differ from those of their stoichiometric counterparts, thereby giving rise to potential ferroelectric polarization properties. However, reports on the emergence of room temperature ferroelectric effects in nonstoichiometric 2D materials remain limited. This study reports the observation of room temperature ferroelectricity in nonstoichiometric AgCr 1‐x S 2 ternary 2D transition metal dichalcogenides synthesized via chemical vapor deposition. The noncentrosymmetric crystal structure and switchable ferroelectric polarization are confirmed through second harmonic generation (SHG) and piezoresponse force microscopy (PFM) measurements. It is determined that the primary cause of ferroelectric polarization is the interlayer movement of ordered asymmetric Ag atoms under the influence of numerous chromium (Cr) vacancies along with interlayer atom displacement. Furthermore, two types of electrical devices based on in‐plane (IP) and out‐of‐plane (OOP) polarization are demonstrated. This work offers a new perspective for fabricating ternary ultrathin 2D transition metal dichalcogenides ferroelectric materials and presents a potential pathway for creating exceptional multifunctional materials.