Engineering moiré bands has established graphene-based superlattices as a highly tunable platform for investigating exotic quantum phases. Most of the focus has been concentrated on the lowest moiré band, and higher-order moiré bands remain largely unexplored because they are typically entangled with other bands and difficult to isolate. A promising route to access this regime is to design systems where high-order moiré bands become energetically isolated and experimentally accessible. Here, we observe multiple well-separated moiré minibands in twisted double-bilayer graphene (tDBG) devices at twist angles ranging from 0.45° to 0.82°. These bands show temperature stability, and multiband features are well captured in theoretically calculated band structures. We further identify correlated insulating states at half-integer fillings (7/2 and 5/2) that persist down to zero magnetic field and display valley-polarized characteristics. These findings suggest that strong correlation in small-angle tDBG extends beyond the lowest moiré band and can persist into higher-order minibands.

This study investigated the electrolytic reduction of kilogram-scale U₃O₈ pellets in molten LiCl and focused on optimizing the process for nuclear fuel cycle applications. Critical developments included resolving carbon impurity issues in LiCl, implementing a sequential kerosene-cyclohexane washing process at 150 °C for lithium anode pretreatment, and establishing optimal pellet fabrication parameters. By adjusting the sintering atmosphere, the pellet density (4.5–8.5 g/cm3) and chemical composition (U₃O₈ or U₄O₉) could be controlled. The electrolytic reduction used a stainless-steel cathode basket loaded with sintered pellets and a lithium metal counter electrode. The experiment was conducted in an inert-atmosphere glove box for 181h. The results showed reduction extents of 99.09

Topological edge/surface states, characterized by spin-momentum locking and topological protection, can provide efficient channels for spin-charge conversion and are valuable for low-power spintronics. Electrostatic tunability, on the other hand, is crucial in both fundamental studies and practical applications of spintronic devices. However, typical topological edge states are gapless and thus the associated spin-charge conversion is generally insensitive to electrostatic gating. Here, we report electrostatically tunable spin-charge conversion in bilayer WTe2, with behavior most consistently explained by a substantial contribution from residual topological edge states. Compared with thicker semimetallic WTe2 reference devices, the bilayer WTe2 exhibits an order-of-magnitude enhancement in conversion efficiency, which can be significantly modulated with gate voltages. Theoretical calculations reveal that, after interlayer hybridization, residual topological edge states with a small energy gap persist in bilayer WTe2 and retain spin-momentum-locked character. The calculated edge-state-related spin Hall conductance is strongly Fermi-level dependent and becomes enhanced near the charge-neutrality regime, consistent with the experimentally observed gate-dependent spin-charge conversion. These results suggest that partially preserved topological edge states can substantially contribute to both enhancement and electrostatic tunability of spin-charge conversion in bilayer WTe2, providing a potential route toward gate-reconfigurable van der Waals spintronic devices.

The coexistence of multiple phases in two-dimensional (2D) materials enables exotic functionalities via inter-phase proximity and charge effects, but the controlled growth mechanism for heterophase 2D superlattices remains elusive. Herein, we successfully grew a highly crystalline self-intercalated 2D 6R-phase TaS2 (ic-2D 6R-TaS2) crystal by chemical vapor transport. A robust in-plane nonlinear Hall effect (NLHE) was observed in low symmetrical ic-2D 6R-TaS2 material (C1v), i.e., 2-3 orders of magnitude higher than WTe2 and MoTe2. Density functional theory (DFT) calculations revealed a strong Berry curvature dipole in the ic-2D 6R-TaS2 crystal, triggered by band crossings near the Fermi level and universally present in a library of ic-2D transition metal dichalcogenide (TMDC) heterophase superlattices, e.g., Nb1+xS2, Ta1+xSe2, etc. Our findings thus provide the atomic insights for the intercalated stabilized growth mechanism of heterophase superlattices and propose a class of ic-2D heterophase TMDC superlattices as potential candidates for NLHE nanodevices.

Extreme light confinement down to the atomic scale has been theoretically predicted for ultrathin, Ta-based transition metal dichalcogenides (TMDs). In this work, we report the observation of highly confined plasmons in 2H-TaS2 monolayers and bilayers via momentum-resolved electron energy loss spectroscopy (q-EELS), with a resolution of 0.0056 Å-1. Momentum-dispersed two-dimensional (2D) plasmon resonances were found to exhibit a lateral confinement ratio up to 300 at large wave vectors of q = 0.15 Å-1 and slow light behaviour with a group velocity ~10-4c. Moreover, we observed a transition from 2D to 3D Coulomb interaction in the high-momentum regime, equivalent to light confinement volumes of 1-2 nm3. Remarkably, the resonant modes do not enter the electron-hole continuum, potentially enabling even further enhanced optical field confinements for this material at cryogenic temperatures.

After decades of research, symmetry breaking in high-temperature cuprate superconductors remains a key issue to resolve and is relevant to understanding their exotic quantum phases. In the prototypical cuprate superconductor, Bi2Sr2CaCu2O8+δ (Bi2212), the possible symmetry breaking has been mostly examined microscopically with scanning tunneling microscopy and photoemission spectroscopy. However, macroscopic evidence and the direct implications for electronic transport have remained elusive. Using superconductivity-enhanced nonreciprocal transport, we report macroscopic evidence of inversion symmetry breaking in Bi2212. While the inversion symmetry breaking is subtle, its effect on nonreciprocal transport is significantly enhanced by the vortex motion during the superconducting transition, leading to a robust manifestation of inversion symmetry breaking in macroscopic transport. Combining angle-resolved nonreciprocal transport and 3D tight-binding model calculations, we derive that the inversion symmetry breaking is due to subtle crystal distortions that give rise to both in-plane and out-of-plane polar axes. Our work not only establishes nonreciprocal transport as a sensitive macroscopic probe to provide electrical transport-based evidence of fine symmetry breaking in Bi2212, but also paves the way for novel device applications such as high-temperature superconducting diodes and superconducting spintronics.

With the explosive expansion of information,there is a growing need for non-volatile memories with high storage density and reconfigurability.Emerging two-dimensional(2D)ferroelectric materials enable the design of various high-performance functional devices that can potentially address these challenges.Here,we report a ferroelectric semiconductor floating-gate transistor based on an α-In2Se3/hexagonal boron nitride(h-BN)/multi-layered graphene(MLG)van der Waals heterostructure on a SiO2/Si substrate.Thanks to the coexistence of both out-of-plane and in-plane polarizations in an α-In2Se3 channel,pairs of polarization-modulated channel resistance states can be successfully generated between the floating-gate-modulated on and off states,which can be programmed by either vertical gate pulses or planar drain pulses.These features enable a 2-bit multi-level memory in both three-terminal or two-terminal operational modes,significantly increasing the storage density and reconfigurability.The present results introduce a new design degree of freedom for floating-gate memories and provide fresh insights into future non-volatile memory technologies.

The nonlinear Hall effect (NLHE) holds immense significance in recognizing the band geometry and its potential applications in current rectification. Recent discoveries have expanded the study from second-order to third-order nonlinear Hall effect (THE), which is governed by an intrinsic band geometric quantity called the Berry Connection Polarizability tensor. Here we demonstrate a giant THE in a misfit layer compound, (SnS)1.17(NbS2)3. While the THE is prohibited in individual NbS2 and SnS due to the constraints imposed by the crystal symmetry and their band structures, a remarkable THE emerges when a superlattice is formed by introducing a monolayer of SnS. The angular-dependent THE and its scaling relationship indicate that the phenomenon could be correlated to the band geometry modulation, concurrently with the symmetry breaking. The resulting strength of THE is orders of magnitude higher compared to recent studies. Our work illuminates the modulation of structural and electronic geometries for novel quantum phenomena through interface engineering.

In alignment with the increasing demand for larger storage capacity and longer data retention, the electrical control of magnetic anisotropy has been a research focus in the realm of spintronics. Typically, magnetic anisotropy is determined by grain dimensionality, which is set during the fabrication of magnetic thin films. Despite the intrinsic correlation between magnetic anisotropy and grain dimensionality, there is a lack of experimental evidence for electrically controlling grain dimensionality, thereby impairing the efficiency of magnetic anisotropy modulation. Here, we demonstrate an electric field control of grain dimensionality and prove it as the active mechanism for tuning interfacial magnetism. The reduction in grain dimensionality is associated with a transition from ferromagnetic to superparamagnetic behavior. We achieve a nonvolatile and reversible modulation of the coercivity in both the ferromagnetic and superparamagnetic regimes. Subsequent electrical and elemental analysis confirms the variation in grain dimensionality upon the application of gate voltages, revealing a transition from a multidomain to a single-domain state, accompanied by a reduction in grain dimensionality. Furthermore, we exploit the influence of grain dimensionality on domain wall motion, extending its applicability to multilevel magnetic memory and synaptic devices. Our results provide a strategy for tuning interfacial magnetism through grain size engineering for advancements in high-performance spintronics.

Extreme light confinement down to the atomic scale has been theoretically predicted for ultrathin, Ta-based transition metal dichalcogenides (TMDs). In this work, we experimentally demonstrate in 2H-TaS_2 monolayers and bilayers a lateral confinement ratio up to 300 at large wave vectors of q = 0.15 Å^-1, and slow light behaviour with a group velocity ∼ 10^-4c. Quantitative momentum-resolved electron energy loss spectroscopy (q-EELS) with a momentum resolution of 0.0056 Å^-1 was used as a platform for the nanoscale optical measurements. With it, momentum-dispersed, two-dimensional (2D) plasmon resonances were experimentally observed, showing a transition from 2D to 3D Coulomb interaction in the high-momentum regime, equivalent to light confinement volumes of 1-2 nm^3. Remarkably, the resonant modes do not enter the electron-hole continuum, predicting even further enhanced optical field confinements for this material at cryogenic temperatures.

Spin injection, transport, and detection across the interface between a ferromagnet and a spin-carrying channel are crucial for energy-efficient spin logic devices. However, interfacial conductance mismatch, spin dephasing, and inefficient spin-to-charge conversion significantly reduce the efficiency of these processes. In this study, it is demonstrated that an all van der Waals heterostructure consisting of a ferromagnet (Fe3GeTe2) and Weyl semimetal enables a large spin readout efficiency. Specifically, a nonlocal spin readout signal of 150 m Omega and a local spin readout signal of 7.8 Omega is achieved, which reach the signal level useful for practical spintronic devices. The remarkable spin readout signal is attributed to suppressed spin dephasing channels at the vdW interfaces, long spin diffusion, and efficient charge-spin interconversion in T-d-MoTe2. These findings highlight the potential of vdW heterostructures for spin Hall effect-enabled spin detection with high efficiency, opening up new possibilities for spin-orbit logic devices using vdW interfaces.

To enhance the extraction of remaining fissile nuclides from spent nuclear fuel through pyrochemical reprocessing, the operational lifetime of such fuels can be extended, ultimately leading to increased cost efficiency and a reduction in the amount of radioactively contaminated waste generated by fast-neutron reactors. Understanding the electrochemical behavior of fissile nuclides in LiCl–KCl is pivotal to the success of molten salt electrorefining pyrochemical reprocessing. In this pursuit, a comprehensive study of Pu(III) salt was conducted to comprehend its electrochemical characteristics within molten chloride salt mixtures. To achieve this, PuCl 3 was meticulously prepared by reacting PuO 2 with HCl in a LiCl–KCl mixture. Subsequently, we investigated the reduction mechanism, the diffusion coefficient of Pu(III) ( D Pu(III) ), and the apparent standard reduction potential of Pu(III)/Pu(0) ( E 0* Pu(III)/Pu(0) ) in situ, using a Mo working cathode. Our findings revealed that Pu(III) undergoes a single-step reduction to Pu(0), involving the exchange of three electrons. Furthermore, the rate of diffusion governs the reduction of Pu(III) at the Mo cathode. The relationship between the diffusion coefficient and temperature was described by ln D = − 5.51 to 4244.2/ T , with an activation energy of 35.28 kJ/mol. Additionally, we examined the temperature-dependent variations of E 0* Pu(III)/Pu(0) and the Gibbs free energy of formation for PuCl 3 (Δ G PuCl3 ). These dependencies were found to be E 0* Pu(III)/Pu(0) = − 3.194 + 6.4 × 10 −4 T and Δ G PuCl3 = − 924.5 + 0.185 T , respectively.

基于固体Al阴极分离锕系元素(An)与裂变产物(FP)的电解精炼技术是极具前景的干法后处理流程之一.本研究采用暂态电化学法系统研究了Pu3+在固体Al阴极上的电化学行为.循环伏安法(CV)和方波伏安法(SWV)研究结果表明,Pu3+在Al阴极上可一步还原为合金,且该反应为不可逆,Pu3+与Al形成合金的电位与温度的关系式为E(Θ),*(Pu3+/PuAln)(vs.Cl-/Cl2)=-2.944+9.84×10-4T.开路计时电位法(OCP)结合相图表明,Pu3+在固体Al阴极上可生成Pu3 Al、PuAl、PuAl2、PuAl3和PuAl4五种合金化合物,且计算得到了不同温度时PuAl4的Gibbs生成自由能.

Emergent quantum phenomena in two-dimensional van der Waal (vdW) magnets are largely governed by the interplay between exchange and Coulomb interactions. The ability to precisely tune the Coulomb interaction enables the control of spin-correlated flat-band states, band gap, and unconventional magnetism in such strongly correlated materials. Here, we demonstrate a gate-tunable renormalization of spin-correlated flat-band states and bandgap in magnetic chromium tribromide (CrBr3) monolayers grown on graphene. Our gate-dependent scanning tunneling spectroscopy (STS) studies reveal that the interflat-band spacing and bandgap of CrBr3 can be continuously tuned by 120 and 240 meV, respectively, via electrostatic injection of carriers into the hybrid CrBr3/graphene system. This can be attributed to the self-screening of CrBr3 arising from the gate-induced carriers injected into CrBr3, which dominates over the weakened remote screening of the graphene substrate due to the decreased carrier density in graphene. Precise tuning of the spin-correlated flat-band states and bandgap in 2D magnets via electrostatic modulation of Coulomb interactions not only provides effective strategies for optimizing the spin transport channels but also may exert a crucial influence on the exchange energy and spin-wave gap, which could raise the critical temperature for magnetic order.

Single-phonon modes offer potential applications in quantum phonon optics, but the phonon density of states of most materials consist of mixed contributions from coupled phonons. Here, using theoretical calculations and magneto-Raman measurements, we report two single-phonon vibration modes originating from the breathing and opposite out-of-plane vibrations of InSe layers. These single-phonon vibrations exhibit an anticorrelated scattering rotations of the polarization axis under an applied vertical magnetic field; such an anomalous magneto-optical behavior is due to the reverse bond polarizations of two quantum atomic vibrations, which induce different symmetry for the corresponding Raman selection rules. A 180° (+90° and -90°) integrated scattering rotation angle of two single-phonon modes was achieved when the magnetic field was swept from 0 to 6 T. This work demonstrates new ways to manipulate the magneto-optic effect through phonon polarity-based symmetry control and opens avenues for exploring single-phonon-vibration-based nanomechanical oscillators and magneto-phonon-coupled physics.

The breaking of multiple symmetries by periodic lattice distortion at a commensurate charge density wave (CDW) state is expected to give rise to intriguing interesting properties. However, accessing the commensurate CDW state on bulk TaS2 crystals typically requires cryogenic temperatures (77 K), which precludes practical applications. Here, we found that heteroepitaxial growth of a 2H-tantalum disulfide bilayer on a hexagonal-boron nitride (h-BN) substrate produces a robust commensurate CDW order at room temperature, characterized by a Moiré superlattice of 3 × 3 TaS2 on a 4 × 4 h-BN unit cell. The CDW order is confirmed by scanning transmission electron microscopy and Raman measurements. Theoretical calculations reveal that the stabilizing energy for the CDW phase of the monolayer and bilayer 2H-TaS2-on-h-BN substrates arises primarily from interfacial electrostatic interactions and, to a lesser extent, interfacial strain. Our work shows that engineering interfacial electrostatic interactions in an ultrathin van der Waals heterostructure constitutes an effective way to enhance CDW order in two-dimensional materials.

Plutonium mononitride is one of the main fuels for Generation IV reactors and can be prepared from nitrogenation of plutonium hydride. We investigated the adsorption and dissociation of nitrogen on PuH2 (111) surface to elaborate the initial stage of nitrogenation. The adsorption energies varied greatly with respect to the adsorption sites and orientations of the adsorbed molecule. The nitrogen exhibited preferential adsorption above the ccp site, where the molecular nitrogen was nearly parallel to the PuH2 surface and pointed to the nearest Pu atom. The orbital hybridization and the electrostatic attraction between the Pu and N weakened the N-N bond in the adsorbed molecule. The mechanism of the dissociation process was investigated within transition state theory, and the analysis of the activation barrier indicated that dissociation of nitrogen is not the rate-determining step of nitrogenation. These findings can contribute to a better understanding of the nuclear fuel cycle.

以金属Ce为原料,对Ce氢化-氮化动力学参数进行研究,分别考察了初始反应温度、原料气体初始压力和Ce片厚度等对金属Ce氢化-氮化反应的影响.研究结果表明:升高初始反应温度有利于缩短氢化过程的诱导时间,但对氢化反应速率无明显影响;提高H2初始压力和降低片层厚度能明显加快氢化反应速率.此外,通过X射线衍射(XRD)和扫描电镜(SEM)等表征证明氢化铈可以与N2反应得到氮化铈(CeN)和H2,但反应需要较高的温度以克服活化能,增加初始反应温度和N2初始压力可以提高反应速率.综合考虑,初始反应温度为350℃、N2初始压力为60 kPa是氢化铈氮化的较优条件.

Quasi-two-dimensional perovskites have emerged as a new material platform for optoelectronics on account of its intrinsic stability. A major bottleneck to device performance is the high charge injection barrier caused by organic molecular layers on its basal plane, thus the best performing device currently relies on edge contact. Herein, by leveraging on van der Waals coupling and energy level matching between two-dimensional Ruddlesden-Popper perovskite and graphene, we show that the plane-contacted perovskite and graphene interface presents a lower barrier than gold for charge injection. Electron tunneling across the interface occurs via a gate-tunable, direct tunneling-to-field emission mechanism with increasing bias, and photoinduced charge transfer occurs at femtosecond timescale (~50 fs). Field effect transistors fabricated on molecularly thin Ruddlesden-Popper perovskite using graphene contact exhibit electron mobilities ranging from 0.1 to 0.018 cm 2 V −1 s −1 between 1.7 to 200 K. Scanning tunneling spectroscopy studies reveal layer-dependent tunneling barrier and domain size on few-layered Ruddlesden-Popper perovskite.

The spin Hall effect (SHE) is usually observed as a bulk effect in high-symmetry crystals with substantial spin–orbit coupling (SOC), where the symmetric spin–orbit field imposes a widely encountered trade-off between spin Hall angle ( θ SH ) and spin diffusion length ( L sf ), and spin polarization, spin current and charge current are constrained to be mutually orthogonal. Here, we report a large θ SH of 0.32 accompanied by a long L sf of 2.2 μm at room temperature in a low-symmetry few-layered semimetal MoTe 2 , thus identifying it as an excellent candidate for simultaneous spin generation, transport and detection. In addition, we report that longitudinal spin current with out-of-plane polarization can be generated by both transverse and vertical charge current, due to the conventional and a newly observed planar SHE, respectively. Our study suggests that manipulation of crystalline symmetries and strong SOC opens access to new charge-spin interconversion configurations and spin–orbit torques for spintronic applications.