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Abstract Two-dimensional (2D) van der Waals (vdW) materials provide the versatile playground to stack two or more vdW layers for creation of superior materials with desired properties. Here we theoretically adopt a twisted stack-engineering of two LaBr2 monolayers to break space inversion symmetry for ferroelectricity and ultimately multiferroism. The enhancement and reversal of electric polarization are accompanied with the transition from interlayer ferromagnetic and antiferromagnetic orderings, demonstrating an effective magnetoelectric coupling effect with a mechanism dissimilar to that of the conventional multiferroics. Magnetization dynamics simulations show that such magnetic phase transition can excite topologically protected bimeron, and the skyrmion Hall effect can be suppressed by bilayer-bimeron stabilized in both ferromagnetic and antiferromagnetic configurations. Moreover, in the small-angle twisted moiré superlattice, the uniform polarization will evolve into a staggered domain structure, accompanied with the appearance of bimeron, which forms a significant discrepancy with the non-twisted stack-engineered multiferroic LaBr2 bilayer. This work provides a strategy for 2D multiferroic materials by twisted stack engineering of magnetic single layers.

Electrical control of topological spin textures is a major goal of spintronics. Here, the authors combine LaCl, a ferromagnet, and In2Se3, a ferroelectric, to create a multiferroic heterostructure, where bimerons, a topological spin-texture, can be created and annihilated by ferroelectric switching.

The perovskite oxide interface has attracted extensive attention as a platform for achieving strong coupling between ferroelectricity and magnetism. In this work, robust control of magnetoelectric (ME) coupling in the BiFeO3/BaTiO3 (BFO/BTO) heterostructure (HS) was revealed by using the first-principles calculation. Switching of the ferroelectric polarization of BTO induce large ME effect with significant changes on the magnetic ordering and easy magnetization axis, making up for the weak ME coupling effect of single-phase multiferroic BFO. In addition, the Dzyaloshinskii-Moriya interaction (DMI) and the exchange coupling constants J for the BFO part of the HSs are simultaneously manipulated by the ferroelectric polarization, especially the DMI at the interface is significantly enhanced, which is three or four times larger than that of the individual BFO bulk. This work paves the way for designing new nanomagnetic devices based on the substantial interfacial ME effect.

Robust control of magnetism is both fundamentally and practically meaningful and highly desirable, although it remains a big challenge. In this work, perovskite oxide superstructures LaFeO3/BaTiO3 (LFO/BTO), LaMnO3/BaTiO3 (LMO/BTO) and LaCrO3/BaTiO3 (LCO/BTO) (001) are designed to facilitate tuning of magnetism by the electric field from ferroelectric polarization, and are systemically investigated via first-principles calculations. The results show that the magnetic ordering, conductivity and exchange interactions can be controlled simultaneously or individually by the reorientation of the ferroelectric polarization of BTO in these designed superstructures. Self-consistent calculations within the generalized gradient approximation plus on-site Coulomb correction did not produce distinct rotations of oxygen octahedra, but there were obvious changes in bond length between oxygen and the cations. These changes cause tilting of the oxygen octahedra and lead to spin, orbital and bond reconstruction at the interface, which is the structural basis responsible for the manipulation. With the G-type antiferromagnetic (G-AFM) ordering unchanged for both ±P cases, a metal–insulator transition can be observed in the LFO/BTO superstructure, which is controlled by the LFO thin film. The LMO/BTO system has A-type antiferromagnetic (A-AFM) ordering with metallic behavior in the +P case, while it shifts to a half-metallic ferromagnetic ordering when the direction of the polarization is switched. LCO/BTO exhibits C-type antiferromagnetic (C-AFM) and G-AFM orders in the +P and −P cases, respectively. The three purpose-designed superstructures with robust intrinsic magnetoelectric coupling are a particularly interesting model system that can provide guidance for the development of this field for future applications.

The nanoscale characteristics of semiconducting transition metal dichalcogenides (TMDCs) are largely determined by their photonic, mechanical, magnetic, thermal, and electronic properties, which can be modulated by adjusting thickness and radiation treatments. In this paper, gamma-rays were applied to irradiate the materials with one to six layers, based on which a comparison was drawn of the frictional and electrical properties before and after irradiation. The changes on a few-layer WSe2 were investigated using Raman spectroscopy, photoluminescence spectroscopy, scanning electron microscopy, transmission electron microscopy, force friction microscopy, and Kelvin probe force microscopy. Under the context of irradiation, there was a phenomenon found different than previously reported. The friction force of WSe2 nano-flakes increased from monolayer to bilayer, decreased at tri-layer, and then increased on a continued basis with thickness. It is suggested that the gamma-ray irradiation treatment could be effective in improving frictional and electronic properties. The range of change to the surface contact potential difference (CPD) was narrowed, and the stability of the device surface potential was enhanced. The continuum mechanics theory was applied to explore the friction force variation between different thickness layers. Based on the puckering effect of tip-flake adhesion, the friction force was determined by bending stiffness. The thermal treatment of WSe2 nanoflakes had a significant impact on the CPD between the sample and the test tip. After thermal treatment, the surface potential increased from one to five layers with thickness. These phenomena were explained in detail. The research contributes to enriching nanotribology and electrical theory in addition to promoting the use of semiconducting TMDCs for nano-components’ design.

Abstract Engineering atomic-scale native point defects has become an attractive strategy to improve the performance of thermoelectric materials. Here, we theoretically predict that Ag-Mg antisite defects as shallow acceptors can be more stable than other intrinsic defects under Mg-poor‒Ag/Sb-rich conditions. Under more Mg-rich conditions, Ag vacancy dominates the intrinsic defects. The p-type conduction behavior of experimentally synthesized α-MgAgSb mainly comes from Ag vacancies and Ag antisites (Ag on Mg sites), which act as shallow acceptors. Ag-Mg antisite defects significantly increase the thermoelectric performance of α-MgAgSb by increasing the number of band valleys near the Fermi level. For Li-doped α-MgAgSb, under more Mg-rich conditions, Li will substitute on Ag sites rather than on Mg sites and may achieve high thermoelectric performance. A secondary valence band is revealed in α-MgAgSb with 14 conducting carrier pockets.

The lattice thermal conductivity ( ${\kappa }_{L}$ ) of the monolayers of partial group-VA elements and binary compounds are systemically investigated by the first-principles calculations and phonon Boltzmann transport equation (PBTE), including aW-antimonene, α -arsenene, black phosphorus, α -SbAs, α -SbP and α -AsP. The ${\kappa }_{L}$ values decrease with the increasing of atomic mass for these materials with similar geometry and valence structures. It is ascribed to phonon branches softening, low phonon group velocity, and large Grüneisen parameters. Due to the neutralization of phonon group velocity and phonon lifetime, ${\kappa }_{L}$ of binary compounds is between their corresponding elements. As the atomic radius and mass increase, the bond strength and the phonon group velocity decreases. Furthermore, the dimensionless parameter ${\gamma }^{2}/A$ , which comes from the Slack equation and only has the dependence of Grüneisen parameter, grows up with the atomic mass rising, which indicates that a larger anharmonicity is present in the heavier V-V monolayers. For SbAs and SbP compounds, the thermal conductivity anisotropy mainly results from the anisotropy of elastic coefficients along armchair and zigzag directions. Our results highlight the impact of atomic arrangement on the thermal conductivity of group VA binary compounds. This work paves a way to modulate the thermal conductivity of 2D VA elements by incorporation atoms with suitable mass and may guide to improve thermoelectrical performance via the alloying method.

Multiple Fano resonances of plasmonic nanostructures have attracted much attention due to their potential applications in multicomponent biosensing. In this paper, we propose a series of hybridized nanostructures consisting of a single nanoring and multiple nanorods to generate multiple Fano resonances. One to three Fano resonances are achieved through tuning the number of nanorods. The interaction coupling process between different components of the nanostructures is recognized as the mechanism of multiple Fano resonances. We also theoretically investigate the applications of the produced multiple Fano resonances in refractive index sensing. The specific properties of multiple Fano resonances will make our proposed nanostructures beneficial to high-sensitivity biosensors. [ABSTRACT FROM AUTHOR]

The thermoelectric property of ZnO is severely limited due to its high thermal conductivity, in spite of its enormously extraordinary characteristics. Two-dimensional (2D) materials usually act as a good strategy to suppress heat transfer by introduction of interfacial scattering in low dimensional systems. The dependence of thermal conductivity on thickness in 2D ZnO is investigated using a first-principle study, combined with the Boltzman phonon transport equation. The thermal conductivity of ZnO for the first three layers sharply decreases with the thickness increasing, which is attributed to the broken phonon selection rule and stronger anharmonicity. The suppressed processes can be reactivated in contrast to the monolayer, such as ZA  +  ZA/ZO ZA/ZO and ZA  +  LA/TA/LO/TO LA/TA/LO/TO. The scattering channels for flexural phonons increase, which suppresses the phonon transport and decreases the thermal conductivity. In addition, the decrease of in-plane interactions outweighs the enhancement of out-of-plane interactions, which leads to the reduced acoustic-optical gap. More A  +  A O phonon scattering may take place and hinder thermal transfer due to a smaller phonon gap. Furthermore, the variation of bond strength in-plane and out-of-plane in multilayer ZnO leads to the reduction of phonon group velocity and the enhancement of anharmonicity. [ABSTRACT FROM AUTHOR]