Frontiers of Physics最新文献

Cluster-assembled materials have long been pursued as they can create some unprecedented and desirable properties. Herein, we assemble a class of one-dimensional (1D) ReNX₄ (X = F, Cl, Br and I) and MF₅ (M = V, Nb and Ta) nanowires by covalently linking their superatomic clusters. These assembled 1D nanowires exhibit outstanding energetic and dynamic stabilities, and hold sizable spontaneous polarization, low ferroelectric switching barriers and high critical temperature. Their superior ferroelectricity is originated from d⁰-configuration transition metal ions generated by the hybridization of empty d orbitals of metal atoms and p orbitals of non-metal atoms. These critical insights pave a new avenue to fabricate 1D ferroelectrics toward the development of miniaturized and high-density electronic devices using building blocks as cluster with precise structures and functionalities.

The values of the low-energy constants (LECs) are very important in the chiral perturbation theory. This paper adopts a Bayesian method with the truncation errors to globally fit eight next-to-leading order (NLO) LECs L ^r_i and next-to-next-leading order (NNLO) LECs C ^r_i . With the estimation of the truncation errors, the fitting results of L ^r_i in the NLO and NNLO are very close. The posterior distributions of C ^r_i indicate the boundary-dependent relations of these C ^r_i . Ten C ^r_i are weakly dependent on the boundaries and their values are reliable. The other C ^r_i are required more experimental data to constrain their boundaries. Some linear combinations of C ^r_i are also fitted with more reliable posterior distributions. If one knows some more precise values of C ^r_i , some other C ^r_i can be obtained by these values. With these fitting LECs, most observables provide a good convergence, except for the πK scattering lengths a ^3/2₀ and a ^1/2₀ . An example is also introduced to test the improvement of the method. All the computations indicate that considering the truncation errors can improve the global fit greatly, and more prior information can obtain better fitting results. This fitting method can be extended to the other effective field theories and the perturbation theory.

The exploration of magnetism in two-dimensional layered materials has attracted extensive research interest. For the monoclinic phase CrI₃ with interlayer antiferromagnetism, finding a static and robust way of realizing the intrinsic interlayer ferromagnetic coupling is desirable. In this work, we study the electronic structure and magnetic properties of the nonmagnetic element (e.g., O, S, Se, N, P, As, and C) doped bi-and triple-layer CrI₃ systems via first-principles calculations. Our results demonstrate that O, P, S, As, and Se doped CrI₃ bilayer can realize interlayer ferromagnetism. Further analysis shows that the interlayer ferromagnetic coupling in the doped few-layer CrI₃ is closely related to the formation of localized spinpolarized state around the doped elements. Further study presents that, for As-doped tri-layer CrI₃, it can realize interlayer ferromagnetic coupling. This work proves that nonmagnetic element doping can realize the interlayer ferromagnetically-coupled few-layer CrI₃ while maintaining its semiconducting characteristics without introducing additional carriers.

We investigate the magnetic excitations of the two-dimensional (2D) S = 1/2 trimerized Heisenberg models with intratrimer interaction J₁ and intertrimer interaction J₂ on four different lattices using a combination of stochastic series expansion quantum Monte Carlo (SSE QMC) and stochastic analytic continuation methods (SAC), complemented by cluster perturbation theory (CPT). These models exhibit quasi-particle-like excitations when g = J₂/J₁ is weak, characterized by low-energy magnons, intermediate-energy doublons, and high-energy quartons. The low-energy magnons are associated with the magnetic ground states. They can be described by the linear spin wave theory (LSWT) of the effective block spin model and the original spin model. Doublons and quartons emerge from the corresponding internal excitations of the trimers with distinct energy levels, which can be effectively analyzed using perturbative calculation when the ratio of exchange interactions g is weak. In this weak g regime, we observe a clear separation between the magnon and higher-energy spectra. As g increases, doublon and quarton gradually merge into the magnon modes or some continua. Notably, in the Collinear II and trimerized Hexagon lattice, a broad continuum emerges above the single-magnon spectrum, originating from the quasi-1D physics due to the dilute connections between chains. In addition, we also compare our numerical results to the experimental RIXS spectrum and analyze the difference. Our numerical analysis of these 2D trimers yields valuable theoretical predictions and explanations for the inelastic neutron scattering (INS) spectra of 2D magnetic materials featuring trimerized lattices.

The simplicity and low-cost way to improve qualitative and quantitative analytical performance has always been a crucial concern for laser-induced breakdown spectroscopy (LIBS), and many scientists have been engaged in this evolving research direction. In this review, we investigated an update on recent developments in light-field modulated operation in LIBS. It covered a brief description of LIBS, optical polarization, and beam shaping. Here, the optical polarization is divided into laser beam polarization and plasma polarization. In addition, the methodology and development of light-field modulated LIBS were summarized and discussed. Finally, the existing problems with light-field modulated LIBS were presented, along with some of their own insights and the future direction of their development. This review will provide a guideline for LIBS researchers with basic knowledge, which is very useful in the signal optimization of LIBS research and applications.

Carbon nanotubes (CNTs) have garnered significant attention due to their remarkable electronic and magnetic properties. In this research, we introduced multiwalled carbon nanotubes covered with tantalum (MWNTs/Ta) to systematically modulate the magnetoresistive properties of the MWNTs/Ta hybrid nanostructures. We observed distinct changes in both positive and negative magnetoresistances of MWNTs/Ta across a broad temperature range using a physical property measurement system and a four-terminal method. This study on temperature-dependent magnetoresistive behavior of the MWNTs/Ta sheds light on the fundamental properties of carbon-based materials and holds promise for practical applications in the field of spintronic devices.

Bilayer (BL) transition metal dichalcogenides (TMDs) are important materials in valleytronics and twistronics. Here we study terahertz (THz) magneto-optical (MO) properties of n-type 2H-stacking BL molybdenum sulfide (MoS₂) on sapphire substrate grown by chemical vapor deposition. The AFM, Raman spectroscopy and photoluminescence are used for characterization of the samples. Applying THz time-domain spectroscopy (TDS), in combination with polarization test and the presence of magnetic field in Faraday geometry, THz MO transmissions through the sample are measured from 0 to 8 T at 80 K. The complex right- and left-handed circular MO conductivities for 2H-stacking BL MoS₂ are obtained. Through fitting the experimental results with theoretical formula of MO conductivities for an electron gas, generalized by us previously through the inclusion of photon-induced electronic backscattering effect, we are able to determine magneto-optically the key electronic parameters of BL MoS₂, such as the electron density n_e, the electronic relaxation time τ, the electronic localization factor c and, particularly, the effective electron mass m* around Q-point in between the K- and Γ-point in the electronic band structure. The dependence of these parameters upon magnetic field is examined and analyzed. This is a pioneering experimental work to measure m* around the Q-point in 2H-stacking BL MoS₂ and the experimental value is very close to that obtained theoretically. We find that n_e/τ/ ∣ c ∣ /m* in 2H-stacking BL MoS₂ decreases/increases/decreases/increases with increasing magnetic field. The results obtained from this study can be benefit to us in gaining an in-depth understanding of the electronic and optoelectronic properties of BL TMD systems.

As the homologous compounds of MoSi₂N₄, the MoSi₂N₄(MoN)_n monolayers have been synthesized in a recent experiment. These systems consist of homogeneous metal nitride multilayers sandwiched between two SiN surfaces, which extends the septuple-atomic-layer MSi₂N₄ system to ultra-thick MSi₂N₄(MN)_n forms. In this paper, we perform a first-principles study on the MoSi₂N₄(FeN) monolayer, which is constructed by iron molybdenum nitride intercalated into the SiN layers. As a cousin of MoSi₂N₄(MoN), this double transition-metal system exhibits robust structural stability from the energetic, mechanical, dynamical and thermal perspectives. Different from the MoSi₂N₄(MoN) one, the MoSi₂N₄(FeN) monolayer possesses intrinsic ferromagnetism and presents a bipolar magnetic semiconducting behaviour. The ferromagnetism can be further enhanced by the surface hydrogenation, which raises the Curie temperature to 310 K around room temperature. More interestingly, the hydrogenated MoSi₂N₄(FeN) monolayer exhibits a quantum anomalous Hall (QAH) insulating behaviour with a sizeable nontrivial band gap of 0.23 eV. The nontrivial topological character can be well described by a two-band k · p model, confirming a non-zero Chern number of C = 1. Similar bipolar magnetic semiconducting feature and hydrogenation-induced QAH state are also present in the WSi₂N₄(FeN) monolayer. Our study demonstrates that the double transition-metal MSi₂N₄(M′N) system will be a fertile platform to achieve fascinating spintronic and topological properties.

Cobalt pnictides have been theoretically proposed to be attractive candidates for high-temperature superconductors. Additionally, monolayered CoX (X = As, Sb, Bi) on SrTiO₃ systems present a potential new platform for realizing topological superconductors in the two-dimensional limit, due to their nontrivial band topology. To this end, we have successfully fabricated high-quality CoBi nanoislands on SrTiO₃ (001) substrates by molecular beam epitaxy followed by an investigation of their atomic structure and electronic properties via in situ scanning tunneling microscopy/spectroscopy. Beyond the previously predicted lattice with a = b = 3.5 Å, 2 × 1 dimer row was observed in this study. Furthermore, our results reveal that the topography of CoBi islands is strongly influenced by various growth conditions, such as substrate temperature, the flux ratio between Co and Bi, and the annealing process. This study paves the way for further explorations of the superconductivity and topological properties of cobalt pnictide systems.