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Searching for two-dimensional materials combining both magnetic order and topological order is of great significance for quantum devices and spintronic devices. Here, a class of two-dimensional transition metal borides, TM2B3 (TM = Ti–Ni), with high stability and stable antiferromagnetic (AFM) orders was predicted by using the first-principles method. The result shows that they possess large magnetic anisotropy energy and high critical temperature. Interestingly, Mn2B3 monolayer is confirmed to be AFM Dirac node line semimetal with several Dirac points near the Fermi level. Detailed analysis of the irreducible representations shows that the nodal lines are protected by the horizontal mirror symmetry Mz. Our findings provide an excellent platform for exploring topological and magnetic materials ready for the next generation of spintronic devices. [ABSTRACT FROM AUTHOR]

In this study, a spring–mass physical model is proposed to study the complex band structure of a one-dimensional parity-time (PT)-symmetric local resonant phononic crystal. By solving the kinetic equations, the analytical solutions of the dispersion relation and effective mass are obtained. As is known, the infinite effective mass would appear at the resonant frequency in a Hermitian system without any gain or loss. Once the balanced gain and loss are added to form a PT-symmetric system, the infinite effective mass would become finite, and the exceptional points can be observed in the subwavelength realm. With the increase in gain and loss, exceptional points would coalesce and form a higher order one. The numerical simulations in a practical structure agree well with the analytical analysis. In addition, the simulated transmission/reflection spectrum and field distribution clearly demonstrate the anisotropic transmission resonances. Our investigation enriches the physical connotation of local resonant phononic crystals in non-Hermitian systems. [ABSTRACT FROM AUTHOR]

Non-Hermiticity extends the topological phase beyond the given Hermitian structure. Whereas the phases of non-Hermitian topological systems derived from Hermitian components have been extensively explored, the topological properties of an acoustic crystal that occur purely due to non-Hermiticity require further investigation. In this letter, we describe the development of an acoustic crystal with an adjustable loss that is composed of a chain of one-dimensional, coupled acoustic resonators. Each unit cell can contain three or six resonators, which are equivalent to 3 × 3 or 6 × 6 non-Hermitian Hamiltonian matrices, respectively. The topological properties of the crystal were verified by calculating the defined topological invariant, and the states of the edge and interface of the acoustic crystal were obtained by using a practical model. We obtained the states of the edges and the interface for both odd and even numbers of resonators in each unit cell and found that the location of the inductive loss had an important effect on the topological properties. This results here can guide research on advanced wave control for sensing and communication applications. [ABSTRACT FROM AUTHOR]

Two dimensional (2D) van der Waals (vdW) heterostructures have recently emerged as attractive candidates in spintronic devices. Here, a field-effect spin filter based on the 2D antiferromagnetic (AFM)/ferromagnetic (FM) vdW heterostructure, MnPS3/MnCl3, is proposed. The ground state of the MnPS3/MnCl3 heterostructure is predicted to be a type-I AFM semiconductor with AFM Néel ordering in MnPS3 and MnCl3 monolayers. Interestingly, an AFM–FM transition is found for the MnPS3/MnCl3 heterostructure when reducing the interlayer distance to the range of d < 2.0 Å. Moreover, the MnPS3/MnCl3 heterostructure undergoes semiconductor, metal, and half-metal transitions with the interlayer distance decreasing. Moreover, a semiconductor–half-metal transition can also be observed for MnPS3/MnCl3 by applying an external electric field. Our study offers a potential way to design spintronic devices by 2D layered magnetic vdW heterostructure. [ABSTRACT FROM AUTHOR]