Advanced Physics Research最新文献

Interfaces between molecular layers and ferromagnetic materials, also called spinterfaces, are the test bed for the development of molecular spintronics, unveiling new effects and opportunities for novel potential applications. Among several combinations of materials that have shown intriguing behaviors, spinterfaces based on antiferromagnetic materials received much less consideration, despite the dramatic increase in attention recently drawn by the antiferromagnetic declination of spintronics. In this work, an antiferromagnetic spinterface based on the transition metal oxide NiO, a widely studied antiferromagnetic insulator with one of the highest critical temperatures, has been realized and characterized. As for the molecular counterpart, Co tetraphenyl porphyrin (CoTPP) is a very promising choice, being sublimable in vacuum and paramagnetic. CoTPP/NiO(001) spinterfaces are experimentally investigated with respect to their morphology, structure, electronic, and magnetic properties. Theoretical calculations have also been performed to circumstantiate and support the measurements. Although characterized by a relatively weak interface coupling, spin-dependent hybridization is observed at the interface, which makes the CoTPP/NiO a perfect system for initiating the exploration of a molecular antiferromagnetic spintronics.

Concealing an aircraft is a multi-faceted endeavor, notably involving radio and infrared frequencies. In a radar stealth context, it often translates to the reduction of the radar cross-section (RCS). However, other routes that take advantage of radar signal processing exist. For instance, a solution has recently been developed, which consists in compensating the motion-induced Doppler shift with a time-modulated metasurface since Doppler radars filter out static targets to avoid being swamped by radar clutter (buildings, trees, etc.). Such a coating, referred to as a Doppler cloak, is able to compensate any frequency shift. However, frequency-modulated radar signals require a broadening of the frequency conversion bandwidth of existing Doppler cloaks, which are all designed for harmonic signals. In this work, the focus is thus placed on a broadband Doppler cloak able to suppress the Doppler information over a wide frequency range. To achieve this, the reflection coefficient of a varactor diode-loaded metasurface is linearized in time to obtain a linear phase ramp necessary to shift the frequency of impinging waves. Numerical and experimental validations are performed using frequency-modulated continuous wave (FMCW) broadband radar signals over the VHF-UHF range.

The burgeoning interest in kesterite materials stems from their promising applications in both charge-selective materials and photocathodes for photoelectrochemical water splitting. Kesterites, a complex class of semiconductors, typically contain copper, zinc, tin, and either sulfur or selenium atoms. Despite their prevalent use as photocathodes, a comprehensive understanding of their optoelectronic properties remains elusive. This study delves into the synthesis and characterization of Copper Zinc Tin Sulfide Selenium (CZTSSe) nanopowders, aiming to elucidate the impact of annealing temperature on their properties. Solution-based synthesis utilizing copper chloride, zinc acetate, tin(II) chloride, and thiourea/selenium precursors yielded CZTSSe nanopowders. Annealing in distilled water at varying temperatures (100 to 350 °C) offers a platform to explore the resulting effects on elemental and phase compositions, morphology, and optical behavior. This research contributes to a deeper understanding of Copper Zinc Tin Selenium (CZTSe) nanopowders and their suitability for photoelectrochemical water splitting, paving the way for further advancements in sustainable energy technologies. This research contributes to a deeper understanding of CZTSSe nanopowders and their suitability for photoelectrochemical water splitting, paving the way for further advancements in sustainable energy technologies.

The main objective of this research article is to investigate the superconductivity properties of Sr_{1 − x}K_xFe₂As₂ superconductor by employing a two-band Hamiltonian model and using Green's function (GF) formalism. Mathematical expressions are derived for key properties such as the superconducting (SC) order parameters, the SC transition temperature, the density of states (DOS), and condensation energy. Utilizing these expressions, Matplotlib in Python is employed to generate phase diagrams illustrating the SC order parameters versus temperature, the SC transition temperature versus SC coupling paramete, the DOS versus excitation energy, and the condensation energy versus the SC transition temperature, temperature, and inter-band pairing potential. These phase diagrams reveal key findings. First, both the SC order parameters and the condensation energy exhibit a decreasing trend as the temperature increases and vanish completely at the SC critical temperature. Second, the DOS initially increases with increasing excitation energy, until it reaches zero temperature SC order parameter (Δ(0)), which corresponds to the energy gap at zero temperature. Beyond this point, the DOS starts to decrease. Finally, the phase diagrams illustrate that the SC transition temperature increases as each intra-inter-band pairing potential increases.

Quantum Anomalies in Dirac Materials

Galaxies hidden in the atoms of Dirac material HfTe₅ illustrate the power of condensed matter platforms to elucidate outstanding questions in cosmological physics, including quantum anomalies. In article 2300111, Elizabeth A. Peterson, Christopher Lane, and Jian-Xin Zhu probe whether the anomalous transport properties of ZrTe₅ and HfTe₅ are potential signatures of a quantum anomaly.

High electron mobility transistors (HEMT) based on Al_1-xSc_xN/GaN and Al_1-xY_xN/GaN heterostructures promise increased device performance and reliability due to the high sheet charge carrier density and the possibility to grow strain-free layers on GaN. Metal–organic chemical vapor deposition (MOCVD) offers high throughput, high structural quality, and good electrical characteristics. The growth of GaN layers on Al_1-xSc_xN and Al_1-xY_xN is challenging, but at the same time crucial as passivation or for multichannel structures. GaN is observed to grow three-dimensionally on these nitrides, exposing not-passivated areas to surface oxidation. In this work, growth of 2–20 nm-thick, two-dimensional GaN layers is demonstrated. Optimization of growth conditions is enabled by understanding island formation on the atomic scale by aberration corrected scanning transmission electron microscopy (STEM) and hard X-ray photoelectron spectroscopy (HAXPES). Increased growth temperature, an AlN interlayer, low supersaturation conditions and the carrier gas are found to be key to enhance Ga adatom mobility. Growth of single crystalline GaN layers on Al_1-xSc_xN and Al_1-xY_xN is unlocked and prevents oxidation of the underlying layers. Few nanometer thick GaN caps allow for depositing the gate metallization directly on the cap, whereas thicker ones allow for the growth of heterostructures for normally-off devices and multichannel structures.

Ultrawide bandgap (UWBG) semiconductors—such as beta gallium oxide (β-Ga₂O₃), aluminum nitride (AlN) and diamond—exhibit exceptional electrical and thermal properties, enabling next-generation power electronics, RF systems, and quantum devices. However, the high power densities and extreme operating conditions of UWBG devices pose significant thermal management challenges. This review provides a comprehensive overview of thermal characterization techniques essential for understanding and mitigating self-heating, thermal bottlenecks, and reliability concerns in UWBG systems. Optical methods such as thermoreflectance imaging, micro-Raman thermometry, and IR thermography, alongside electrical approaches like gate resistance thermometry (GRT) and micro thin-film thermocouples (micro-TFTCs), are critically compared in terms of resolution, sensitivity, and application scope. The review also highlights recent advancements in hybrid techniques and material innovations to enhance heat dissipation. By evaluating the strengths and limitations of each method, this paper guides the selection of suitable thermal metrology tools for diverse UWBG device architectures and operating environments, facilitating their practical deployment in high-performance electronics.

Shortly after the discovery of topological band insulators, topological Kondo insulators (TKIs) is also theoretically predicted. The latter has ignited revival interest in the properties of Kondo insulators. Currently, the feasibility of topological nature in SmB₆ is intensively analyzed by several complementary probes. Here by starting with a minimal-orbital Anderson lattice model, the local electronic structure is explored in a Kondo insulator. It is showed that the two strong topological regimes sandwiching the weak topological regime give rise to a single Dirac cone, which is located near the center or corner of the surface Brillouin zone. It is further found that, when a single impurity is placed on the surface, low-energy resonance states are induced in the weak scattering limit for the strong TKI regimes and the resonance level moves monotonically across the hybridization gap with the strength of impurity scattering potential; while low energy states can only be induced in the unitary scattering limit for the weak TKI regime, where the resonance level moves universally toward the center of the hybridization gap. These impurity-induced low-energy quasiparticles will lead to characteristic signatures in scanning tunneling microscopy/spectroscopy, which has recently found success in probing into exotic properties in heavy fermion systems.

Emerging Cellulose Ionogels

Through the physical construction of molecular network structures, soft gel materials derived from biomass cellulose can acquire a range of distinctive properties and be used in high-value applications. Article number 2500020 by Xiaoyu Guo, Suqing Zeng, Dawei Zhao and co-workers explores the design of functional gels through molecular-scale physical enhancement methods, thereby broadening the potential applications of cellulose gels in emerging flexible electronics. The integration of attractive physical processing techniques with molecular-scale design represents a promising research avenue for cellulose gels. This study provides valuable insights for the future development of smart gels and wearable devices.