摘要 : The van der Waals (vdW) material Fe 5 GeTe 2 is a promising candidate for spintronic applications due to its high Curie temperature ( T C ) and easily controllable properties. In this study, we thoroughly investigate the magnetic anisotropy of Fe 5 GeTe 2 single crystals using magnetization and electron spin resonance (ESR) techniques. We find that the magnetization for H / / a b is stronger than that for H / / c below T ∗ ∼ 100 K, exhibiting a weak easy-plane anisotropy (EPA). This EPA is significantly enhanced in the temperature range of T ∗ < T < T C, indicating an enhanced EPA effect. Meanwhile, the ESR spectra show weak intensity below T ∗ while significantly anisotropic signals are observed in the enhanced EPA region, with stronger ESR intensity for H / / a b compared to that for H / / c . The resonance fields ( H r ) for H / / a b and H / / c display opposite trends. The resonance field H r a b for H / / a b shifts toward lower fields, while H r c for H / / c moves toward higher fields upon cooling. This contrary trends of H r for H / / a b and H / / c are attributed to the effects of magnetocrystalline anisotropy and shape anisotropy, which are consistent with observations in two-dimensional ferromagnetic materials with EPA. These findings enhance our understanding of the magnetic correlations and spin dynamics in this system.

摘要 : The family of materials exhibits excellent thermal and mechanical stability, unique electronic properties, and ultrahigh carrier mobility, rendering them highly promising for low-dimensional nanodevice applications. Using atomic substitution modeling, we computationally investigate the structural configurations of - and -phase in three monolayers:, , and -. Our first-principles analysis reveals that these monolayers possess robust structural and mechanical stability alongside high carrier mobility, making them ideal candidates for next-generation nanoelectronics. Specifically, the simulations of pn-junction diodes based on Janus monolayers demonstrate excellent rectification effects, while -phase pn-junction diodes exhibit negative differential resistance at finite bias. Furthermore, the pin-junction field-effect transistors show distinct behavior under positive and negative gate voltages, and the associated phototransistors display robust photovoltaic responses in the violet and ultraviolet regions, underscoring their significant optoelectronic potential. These results demonstrate the potential of Janus -based monolayers for future high-performance electronic and optoelectronic applications.

摘要 : Two-dimensional (2D) transition metal dichalcogenides (TMDs) are becoming increasingly attractive and beneficial to the development of spintronic devices and integrated circuit technologies. The magnetism of monolayer vanadium disulfide remains debated, with no consensus on whether it exhibits ferromagnetism or remains non-magnetic at room temperature. Herein, based on first-principles calculations, we study the stability and electronic structure of monolayer VS 2 in the 1T and 2H phases. Both phases are ferromagnetic ordering in the ideal structure and the magnetic exchange parameters are obtained through the spin-spiral method. Moreover, through the Monte Carlo simulator, we simulate the variation of magnetic parameters along with the increase in temperature. Finally, according to the Stoner criterion, the magnetic moment around the V point defect may collapse due to the decrease in the density of states at the Fermi level. This provides a theoretical explanation for the prevalent absence of observation of net magnetic moments in experiments.

摘要 : Two-dimensional (2D) honeycomb lattices provide a versatile platform for realizing topologically nontrivial states. In this work, we uncover the coexistence and electrical tunability of quantum anomalous Hall (QAH) and quantum spin Hall (QSH) states in 2D honeycomb lattices characterized by non-Dirac band structures. Employing a tight-binding model, we demonstrate that px and py orbitals lead to quadratic non-Dirac band degeneracies at the Γ point and linear Dirac band degeneracies at the K and K′ points. The introduction of a magnetic exchange field and atomic spin-orbit coupling can induce distinct QAH and QSH gaps at separate energy levels within the same system. First-principles calculations validate these findings in a ferromagnetic monolayer of functionalized plumbene (Pb2⁢BrO), predicting sizable QAH (175.4 meV) and QSH (187.8 meV) gaps. Notably, the Fermi energy of monolayer Pb2⁢BrO resides in the QAH gap but can be electrically gated into the QSH gap, enabling reversible transitions between these two topologically nontrivial states. These results provide a theoretical foundation for the design of electrically tunable topological materials and establish 2D honeycomb lattices with non-Dirac bands as a promising platform for multifunctional quantum applications.

摘要 : Kagome materials, which are composed of hexagons tiled with a shared triangle, have inspired enormous interest due to their unique structures and rich physical properties; exploring superconducting material systems with new kagome structures is still an important research direction. Here, we predict a type of kagome superconductor, M⁢Pd5 (M is a group-IIA metal element), and identify that it exhibits coexistence of superconductivity and nontrivial topological properties. We uncover its phonon-mediated superconductivity by the density functional theory for superconductors, predicting the superconducting transition temperatures (Tc) of 2.64, 2.03, and 1.50 K for CaPd5, SrPd5, and BaPd5, respectively. These Tc can be effectively tuned through the application of external pressure and electron doping. The present results also demonstrate that M⁢Pd5 have topological properties; e.g., CaPd5 shows topological nontrivial intersection near the Fermi level (EF). Our results indicate that M⁢Pd5 materials can be an emerging material platform with rich exotic physics in their kagome structures, and render themselves excellent candidates for superconducting and advanced functional materials that could be utilized in topological quantum computing and information technology.

摘要 : Two-dimensional (2D) MXene nanomaterials have shown great promise for electronic devices, attributed to their metal-resembling conductivity and abundant surface functional groups. However, the utilization of intrinsic property of MXene in memristors remains challenging due to its free electron conducting behavior rather than semiconducting property. Here, a N-fused perylenediimide organic semiconductor (CBIN) with conjugated skeleton and heteroatoms (O, S, N) is designed to successfully actuate the surface modification of MXene. The organic CBIN-decorated MXene demonstrates remarkable bipolar memristive properties, such as low threshold voltages of approximate ±1.4 V, exalted retention time exceeding 104 s, and outstanding environmental stability even after exposure to ultraviolet and x-ray irradiations. Furthermore, the CBIN-MXene hybrid memristive device can mimic synaptic plasticity and holds potential for information encoding as quick response codes and image recognition processing. This study provides efficient guidelines for implementing MXene-based memristors by organic semiconductor modulation and opens up possibilities of extending their functionalities into information encryption and neuromorphic computing applications.

摘要 : MXenes are emerging two-dimensional (2D) nanomaterials comprising multiple atomic layers of transition metal carbides/nitrides/carbonitrides. However, due to the metallic analogous conductivity, their intrinsic application in electronic devices is restricted. In this work, it is discovered that the straightforward surface modification of MXene holds promise for extending its functionality into the semiconductor field. The zero-dimensional carbon quantum dots (0D-CDs) are designed and adopted to allow the surface modification of MXene. The uniformly distributed CDs are introduced to function as charge storage elements, thereby enhancing charge transport process, reducing power consumption, and improving stability of MXene-based electronics. Notably, the CDs-modified MXene memristor exhibits outstanding bidirectional tunable memristive performance and replicates synaptic plasticity behavior, which facilitates the development of electronic synapses. This study unveils the potential of applying MXene for high-performance memristors through CDs modulation strategy, and provides an effective pathway for expanding the metallic conductive 2D nanomaterials into non-volatile memory and artificial synapses.

摘要 : Heterojunctions of two-dimensional (2D) materials have generated substantial research interest due to their diverse and novel properties. In this study, we propose a class of superconductor-semiconductor-superconductor (SSS) lateral heterojunction diodes based on M⁢Si2⁢N4 (M = Ta, Mo, W) monolayers. Using the ab initio method, we simulate the time- and angle-resolved photoelectron spectroscopy (Tr-ARPES) for all M⁢Si2⁢N4 monolayers and, importantly, reveal the one-band and two-gap s-wave superconductivities in Ta⁢Si2⁢N4. Furthermore, these SSS diodes exhibit a significant and tunable negative differential resistance (NDR) effect. Our findings suggest that M⁢Si2⁢N4 monolayers are promising platforms for studying superconducting materials and NDR-based nanodevices, further broadening the potential applications of the MA2⁢Z4 family of materials in nanoelectronics.

摘要 : SrTiO3 (STO) displays a broad spectrum of physical properties, including superconductivity, ferroelectricity, and photoconductivity, making it a standout semiconductor material. Despite extensive research, the oxygen partial pressure-dependent conductivity in STO has remained elusive. This study leverages first-principles calculations and systematically investigates the intrinsic defect properties of STO. The results reveal that VO, VSr, and TiSr are the dominant intrinsic defects, influencing STO's conductivity under varying O chemical potentials (oxygen partial pressures). Under O-poor condition, VO is the predominant donor, while VSr is the main acceptor. As the oxygen pressure increases, TiSr emerges as a critical donor defect under O-rich conditions, significantly affecting the conductivity. Additionally, the study elucidates the abnormal phenomenon where VTi, typically an acceptor, exhibits donor-like behavior due to the formation of O-trimer. This work offers a comprehensive understanding of how intrinsic defects tune the Fermi level, thereby altering STO's conductivity from metallic to n-type and eventually to p-type across different O chemical potentials. These insights resolve the long-standing issue of oxygen partial pressure-dependent conductivity and explain the observed metallic conductivity in oxygen-deficient STO.

摘要 : The critical exponents of the HoNi2 intermetallic alloy have been precisely obtained from the modified Arrott plots and the Kouvel-Fisher method, with values: β = 0.215, γ = 0.748, and δ = 4.489. With these values of the critical exponents, the isothermal magnetization M (μ0H) curves collapse below and above the Curie temperature (TC = 14 K) into two universal branches, fulfilling the single scaling equation m=f±(h), where m and h are the normalized magnetization and normalized magnetic field, respectively. The reliability of the critical exponents was confirmed by the Widom scaling hypothesis δ=1+γ/β, indicating that they are unambiguous and intrinsic to HoNi2 compound. This set of critical exponents lies between the theoretical values predicted by 3D and 2D models, suggesting a dimensional crossover between them. The primary reason for the nature of the determined critical behavior is linked to the tetrahedral local environment of Ni atoms within the unit cell.