Advanced Physics Research最新文献

Tunneling techniques are pivotal for probing 2D magnetic materials. While the Fowler-Nordheim model describes tunneling in bulk materials through bias-induced triangular potentials, van der Waals layered systems require special consideration of interlayer gaps. The fundamental mechanisms of tunneling processes in van der Waals magnetic materials are delved into, with a specific emphasis on CrBr₃. Layer-resolved quasi-resonant tunneling (QRT) mediated by ladder-shaped barriers is revealed. QRT occurs because the outermost CrBr3 conduction band aligns with the Fermi level of the tunneling electrode under the bias voltage tilting, resulting in an increased tunneling probability and enhanced current. Two competing mechanisms driven by the magnetic field—the suppression of spin fluctuations leading to negative tunneling magnetoresistance (TMR) and the spin-flip-induced elevation of the conduction band energy causing positive TMR—are identified to explain the diverse behaviors of tunneling magnetoresistance under different bias voltages and temperatures. The work establishes van der Waals heterostructures as distinct tunneling systems differing fundamentally from conventional bulk barriers, while introducing the QRT concept as a critical advancement in understanding electronic tunneling in layered materials.

Two-dimensional (2D) ferroelectrics, especially lead-free materials such as barium titanate, BaTiO₃, hold significant promise for advanced electronics due to their unique nanoscale properties. Doping BaTiO₃ with lanthanides (Ln) can enable fine-tuning of electrical and dielectric properties by substituting Ba²⁺ (A-site) or Ti⁴⁺ (B-site) in the perovskite structure. A-site doping enhances dielectric properties, while doping the B-site changes the polarization and thermal stability. The site preference depends on the ionic radii and charge compensation mechanisms, which include oxygen vacancies and self-compensation processes. This research delivers the structural and microstructural aspects of BaTiO₃ doped with members of the Ln family from La to Lu, emphasizing their superior properties compared to undoped BaTiO₃. Notably, the Ln dopants significantly influence the ferroelectric, ferromagnetic, luminescent, and piezocatalytic properties, where the ionic radius, doping mechanisms, defect formation, and preparation methods play a role. Theoretical studies and advanced characterization data indicate that Ln dopants improve the performance of BaTiO₃ by stabilizing structural defects, affecting site occupancy, and improving insulation resistance. Understanding the defect chemistry and Ln ion distribution in Ln-doped BaTiO₃ systems can help optimize their functional properties for next-generation technologies and sustainable energy applications.

The Ruddlesden-Popper 5d iridate Sr₂IrO₄ is an antiferromagnetic Mott insulator with the electronic, magnetic, and structural properties highly intertwined. Voltage control of its magnetic state is of intense fundmenatal and technological interest but remains to be demonstrated. Here, the tuning of magnetotransport properties in 5.2 nm Sr₂IrO₄ via interfacial ferroelectric PbZr_0.2Ti_0.8O₃ is reported. The conductance of the epitaxial PbZr_0.2Ti_0.8O₃/Sr₂IrO₄ heterostructure exhibits ln(T) behavior that is characteristic of 2D correlated metal, in sharp contrast to the thermally activated behavior followed by 3D variable range hopping observed in single-layer Sr₂IrO₄ films. Switching PbZr_0.2Ti_0.8O₃ polarization induces nonvolatile, reversible resistance modulation in Sr₂IrO₄. At low temperatures, the in-plane magnetoresisance in the heterostructure transitions from positive to negative at high magnetic fields, opposite to the field dependence in single-layer Sr₂IrO₄. In the polarization down state, the out-of-plane anisotropic magnetoresistance R_AMR exhibits sinusoidal angular dependence, with a 90° phase shift below 20 K. For the polarization up state, unusual multi-level resistance pinning appears in R_AMR below 30 K, pointing to enhanced magnetocrystalline anisotropy. The work sheds new light on the intriguing interplay of interface lattice coupling, charge doping, magnetoelastic effect, and possible incipient ferromagnetism in Sr₂IrO₄, facilitating the functional design of its electronic and material properties.

Singular Electromagnetics

A vortex of twisted light beams serves as a streamline to organize and present the primary research objectives of singular electromagnetics/singular optics. As reviewed by Jiafu Wang, Xuezhi Zheng and co-workers in article number 2400083, these objectives include phase singularities in complex scalar fields, polarization singularities in complex vector fields, and 3D topological defects (specifically, four types are presented: optical skyrmions, hopfions, knots, and Möbius strips). These research objectives are well-recognized within the communities of electromagnetics, optics, photonics, metamaterials, and plasmonics, as well as acoustics, while also capturing the attention of a broader audience from other research fields or even non-research readers.

Electrical Control of Excitonic Complexes

The cover feature showcases the exploration of exciton complexes in electrically contacted artificially twisted MoSe₂ homobilayers, highlighting their unique optical and electronic properties. Unlike conventional heterobilayers, homobilayers benefit from the absence of lattice mismatch, enhancing their potential for practical applications. In article number 2400135, Bárbara L. T. Rosa, Stephan Reitzenstein and colleagues unveil the tunable excitonic behavior of these systems through electrical charge carrier concentration control at room temperature. By performing gate-dependent photoluminescence experiments on devices with various twist angles, they demonstrate a twist-angle-dependent doping effect that significantly influences the neutral and negatively charged intralayer excitons. The findings substantially advance the understanding of TMD homobilayers by enabling control over their emission properties, laying a strong foundation for future applications in van der Waals semiconductor devices.

Magnetic skyrmions with unique topological spin textures, hold great promise for spintronic devices. In particular, the circular motion of skyrmions has shown potential as nanoscale oscillators for radio frequency applications. This study introduces a skyrmion-based oscillator driven by surface acoustic waves (SAWs) through magnetoelastic coupling. Using micromagnetic simulations, precise tunability of the oscillator's frequency is demonstrated by varying the strain amplitude induced by a SAW and device dimensions. Furthermore, incorporating two skyrmions into the device significantly broadens the frequency tuning range. The proposed design offers a promising pathway for advancing nanoscale microwave frequency converters and spread spectrum modulation technologies.

Cellulose gels, including ionic gels, hydrogels, and aerogels, are 3D, soft polymeric materials known for their excellent properties and designability. As sustainability and green chemistry gain prominence, performance improvement and functional design of cellulose gels have attracted growing attention. The macroscopic physical properties of cellulose gels can be shaped by constructing a gel network, which can be regulated by physical methods such as freezing, force induction, and heat treatment to adjust the mechanical properties, transparency, and thermal stability of cellulose. Additionally, structural design and self-assembly of cellulose at the molecular level can endow cellulose gels with diverse functions, such as stretchability, high toughness, ionic conductivity, and self-healing ability. These characteristics give them broad application potential in biomedicine, flexible electronics, adsorption, and food engineering. This article delves into the fundamental concepts, physical properties and design, enhancement methods, molecular strategies, and trending applications of cellulose-based gels across various fields. It provides a comprehensive overview of this promising material and offers insights and guidance for future research and development.

Line defects, dislocations, in ferroelectric materials can facilitate the nucleation of new domains and pin the motion of domain walls, leading to significant electromechanical responses. However, the mechanisms that how dislocations influence surrounding atoms and domains remains unclear. In this study, the influence of mechanically introduced {100}<100> dislocations on atomic polarization and the evolution of domain structures under an applied electric field is examined using aberration-corrected transmission electron microscopy (TEM), paired with solid-state nuclear magnetic resonance and synchrotron X-ray diffraction. The results indicate that dislocations affect the polarization of surrounding atoms and domain pattern depending on the inhomogeneous distribution of dislocations. Additionally, dislocation lines may overlap with or pin domain walls, thereby significantly influencing the evolution of domain structures. Furthermore, in situ electric field TEM experiments provided clear evidence of domain structure changes, demonstrating that dislocations can serve as nucleation sites and anchors for domain walls.

In the field of evaluating the parameters of the weapon, since the true value of the velocity of the projectile under measure is unknown, the method of absolute metrology for the accuracy of the optoelectronic velocity measuring systems cannot be achieved. In response to this problem, this paper constructs the system and method for simulating the generation of optical signals for projectiles passing through the target. The mathematical modeling of the process of the projectile passing through the target is carried out, and the virtual instrument is used to generate the ideal signal of the projectile with adjustable size and velocity required, and then use the acoustooptic modulation technology to modulate the laser intensity, thereby simulating the optical signal of the projectile during the operation of the measuring system in the environment of live fire shooting. The results show that the simulation of the signals can be achieved with a linear correlation coefficient of up to 90%. Therefore, use this signal to input to the detection terminal of the optoelectronic velocity measuring systems to simulate the projectile passing through the measuring screen, the performance parameters of the measuring system can be verified and tested in the indoor laboratory.