Ting Yu

Ruthenium oxides have been the model catalyst for the acidic oxygen evolution reaction. It has been a challenge to achieve both stability and activity and establish a comprehensive descriptor for Ru-based catalysts. Herein, guided by the ligand field theory, we introduce the Ru orbital splitting energy (ΔRu) as a quantitative parameter to describe the interaction between Ru 4d and O 2p orbitals to govern the overall catalytic performance. A series of two-dimensional (2D) multielement metal oxides are synthesized via a self-assembly method to modulate ΔRu. The optimized RuCoFeNiO catalyst for water oxidation delivers a current density of 10 mA cm–2 at a low overpotential of 180 mV and shows high activity for more than 2500 h at 1 A cm–2 in acidic condition. In situ measurements and theoretical analysis reveal that the surface hydrogen-bond network balances the amount of surficial two-hydrogen-bonded water and free water, boosting the proton-transfer process. Moreover, the optimized ΔRu (2.405 eV) modifies the adsorption of *OOH on Ru sites, switching the dominant reaction pathway from the lattice oxygen mediated mechanism to absorbate evolution mechanism. This work highlights the pivotal role of ΔRu in tailoring both stability and activity and may offer insights into high-entropy 2D Ru-based oxides as high-performance oxygen evolution electrocatalysts.

Brillouin-zone-edge phonons are of great significance to many-body interactions and intervalley dynamics in two-dimensional (2D) materials. However, probing these elusive modes typically relies on destructive defect engineering for relaxing fundamental momentum conservation. Here, we establish a non-destructive and tunable paradigm by constructing a van der Waals heterostructure of few-layer MnPS₃ and monolayer WSe₂, which induces the emergence of giant anomalous Raman responses from large-momentum phonons from the intact WSe₂ lattice. Based on comprehensive spectroscopic investigations, we propose a phenomenological framework suggesting that this phenomenon is driven by a synergistic structural-electronic mechanism. We postulate that the massive lattice mismatch between few-layer MnPS₃ and monolayer WSe₂ creates a highly incommensurate interface, which provides necessary momentum compensation. Meanwhile, we suppose that the highly localized Mn 3d flat band acts as an energy-matched resonant amplifier. Crucially, we demonstrate the potential tunability of this system through the h-BN spacer insertion and elemental substitutions (FePS₃ and NiPS₃). These manipulations corroborate our hypothesis, allowing modulation of the anomalous responses from giant amplification to complete suppression via deliberate energy detuning. The ability to probe and modulate these fundamental mediators of many-body interactions in a non-destructively way establishes a robust framework for developing advanced 2D quantum phononic architectures.

Two-dimensional transition metal chalcogenides have attracted significant interest for advanced functional materials due to their tunable electronic structures and polymorphic phase transitions. However, achieving dynamically switchable room-temperature ferroelectricity remains a significant challenge. Here, we demonstrate that Ar⁺ ion beam irradiation induces controlled Te vacancies in monolayer 2H-MoTe₂, triggering robust out-of-plane ferroelectric polarization at 300 K. Through polarization-resolved second-harmonic generation (SHG) microscopy and low-temperature spectroscopic characterization, we verify the ion-beam-induced symmetry breaking and the formation of nonuniform ferroelectric domains with switchable polarization states. Comprehensive switching spectroscopy piezoresponse force microscopy (SS-PFM) with rigorous artifact mitigation reveals reversible 180° polarization switching, confirmed by characteristic phase hysteresis and symmetric amplitude butterfly loops. Crucially, polarity-dependent linear sweep voltammetry (LSV) demonstrates that hydrogen evolution reaction (HER) activity can be reversibly modulated by polarization switching: positive poling reduces the overpotential, while negative poling degrades it, establishing a direct causal link between ferroelectric state and catalytic performance. Remarkably, this defect-engineered ferroelectric polarization modifies the interfacial charge distribution, optimizing the hydrogen adsorption free energy (ΔG_H*) from 1.86 eV (pristine) to −0.27 eV (irradiated), thereby significantly enhancing the hydrogen evolution reaction (HER) activity. This work establishes ferroelectric polarization as a primary descriptor for electrocatalytic enhancement and provides a defect-engineering strategy for designing adaptive nanocatalysts.

Emerging two-dimensional magnetic semiconductors represent transformative platforms to explore magneto-optics and opto-spintronic applications. Though two-dimensional opto-spintronics has attracted tremendous research efforts in spin-dependent photodetectors and non-volatile memory components, the realization of one core application - spin-modulated light-emitting device - remains elusive so far. Here, we successfully realize prototype spin-modulated light-emitting device integrated with a two-dimensional semiconducting magnet chromium sulfide bromide, demonstrating considerable electroluminescence down to bilayers. Intriguingly, it's discovered to be directly manipulated by spin-flip and spin-canting transitions. Notably, the intrinsic carrier-tunable interlayer magnetic coupling in chromium sulfide bromide enables electroluminescence to actively amplify magnetic hysteresis (via spin-flip) and continuously tune magnetic order (via spin-canting) with robust anisotropy, establishing a connection between carrier injection, magnetic phase transitions, and optical emission. The prototype demonstration of spin-modulated light-emitting device establishes an indispensable scheme of opto-spintronic devices leveraging two-dimensional spin transitions and strong excitonic effects, presenting a critical step towards integrated two-dimensional opto-spintronics.

Room-temperature skyrmions in the two-dimensional (2D) van der Waals (vdW) ferromagnet Fe₃GaTe₂ (FGaT) hold great promise for spintronics. However, the origin of the necessary Dzyaloshinskii-Moriya interaction (DMI) within its centrosymmetric lattice remains elusive. Here, we reveal a spontaneous DMI emergence mechanism driven by field cooling (FC) in FGaT and its analog Fe₃GeTe₂ (FGeT). We show that the commonly used FC process causes the irreversible precipitation of FeTe₂ layers on the FGaT surface. This FeTe₂/FGaT heterostructure breaks the inversion symmetry, generating a finite interfacial DMI. This phenomenon extends to analogous FGeT, demonstrating its universality. Notably, a threshold thickness governs effective FeTe₂ precipitation and subsequent skyrmion formation. Leveraging these findings, we developed an optothermal technique to deterministically write single skyrmions in FGaT without FC. Our findings provides new insights into DMI origins and skyrmion manipulation in ternary tellurides, paving the way for advanced spintronic applications.

Exciton quantum phases of Bose-Einstein condensation, exciton insulators, and superfluidity are largely governed by exciton-exciton interactions. Manipulating these interactions has sparked tremendous efforts to investigate quantum-confined excitons in two-dimensional (2D) semiconductors. In typical 2D exciton systems, however, strong dipolar interactions can be accessible at the cost of optical deactivation with significantly reduced oscillator strengths. Here we observe an emergent dipolar exciton with strong interactions in 2D perovskites with a surface lattice reconstruction. To unravel the microscopic nature of this exciton, we synergistically combine extensive optical spectroscopy, quantum-confined Stark effect, and density functional theory calculations. The dipolar exciton features dominant in-plane (IP) transition dipole moments, alongside coexisting out-of-plane (OP) electric dipole moments, giving rise to an exciton-exciton interaction strength of 38.1 ± 6.7 μeV·μm² as one of the highest reported to date. The observation promises great potential to explore quantum phenomena and optoelectronic applications based on strongly interacting dipolar excitons in 2D semiconductors.

The emergence of two-dimensional (2D) van der Waals (vdW) ferromagnets has opened new avenues for exploring topological spin textures and their applications in next-generation spintronics. Among these materials, Fe3GaTe2 (FGaT) emerges as a model system due to its room-temperature skyrmion phases, which are stabilized by strong Dzyaloshinskii-Moriya interaction (DMI). However, the atomistic origins of DMI in centrosymmetric vdW lattices remain elusive. Here, we report a spontaneous DMI enhancement mechanism driven by field cooling (FC) in FGaT and its analog Fe3GeTe2 (FGeT). Combining Raman spectroscopy and scanning transmission electron microscopy (STEM), we reveal that the commonly used FC process causes the irreversible precipitation of FeTe2 thin layers at the surfaces of the annealed FGaT. The resulted FeTe2/FGaT heterostructure breaks the inversion symmetry and significantly enhances the DMI. Similar phenomenon has been observed in the family ferromagnetic material FGeT as well, indicating the universality of this mechanism. Additionally, we note there is a threshold thickness of FGaT for the effective precipitation of FeTe2 and further formation of skyrmions. Based on our new findings and to further demonstrate the application potential of FGaT in future spintronics, we successfully develop a facile technique to write and pattern single skyrmions in FGaT at room temperature and without FC process. The discovery provide new insights into the mechanisms behind the origin of the DMI and manipulation of skyrmions in ternary tellurides, paving the way for advanced spintronic applications.

Emerging two-dimensional (2D) magnetic semiconductors represent transformative platforms to explore magneto-optics and opto-spintronic applications. Though 2D opto-spintronics has attracted tremendous research efforts in spin-dependent photodetectors and non-volatile memory components, the realization of one core application -spin-modulated light-emitting device (spin-LED)- remains elusive so far. Here we successfully realize prototype spin-LED integrated with a 2D semiconducting magnet CrSBr, demonstrating considerable electroluminescence (EL) down to bilayers. Intriguingly, the EL of the spin-LED is discovered to be directly manipulated by spin-flip and spin-canting transitions. Notably, spin-flip transitions enable unprecedented hysteretic behaviors of EL characteristics, while spin-canting transitions induce EL continuous modulation with robust anisotropy. This versatile manipulation is originated from the synergy of magnetic-order mediated excitonic transitions and spintronic transport. The prototype demonstration of spin-LED establishes an indispensable scheme of opto-spintronic devices leveraging 2D spin transitions and strong excitonic effects, presenting a critical step towards integrated 2D opto-spintronics.

Manipulating topological magnetic orders of 2D magnets by strain, once achieved, offers enormous potential for future low‐power flexible spintronic applications. In this work, by placing Fe ₃ GaTe ₂ (FGaT), a room‐temperature 2D ferromagnet, on flexible substrate, a field‐free and robust formation of skyrmion lattice induced by strain is demonstrated. By applying a minimal strain of ≈0.80% to pre‐annealed FGaT flakes, the Magnetic Force Microscopy (MFM) tip directly triggers the transition from maze‐like domains to an ordered skyrmion lattice while scanning the sample surface. The skyrmion lattice is rather stable against extensive cyclic mechanical testing (stretching, bending, and twisting over 2000 cycles each). It also exhibits stability across a wide range of magnetic fields (≈2.9 kOe) and temperatures (≈323 K), as well as long‐term retention stability, highlighting its robustness and field‐free stabilization. The strain effect reduces the lattice symmetry and enhances the Dzyaloshinskii‐Moriya interaction (DMI) of FGaT, thus stabilizing the skyrmion lattice. The findings highlight the potential of FGaT for integrating magnetic skyrmions into future low‐power‐consumption flexible spintronics devices.