Spin and valley transport in n-p-n junction of borophene

Abstract

With attention to the importance of two-dimensional materials in nanoelectronics and spintronics, we study a very thin layer of boron, known as borophene. Several stable allotropes of borophene including α sheet, β sheet, β12 sheet, 8-pmmn borophene, and so on have been introduced by researchers [1]. Among them, the 8-pmmn borophene with 8 atoms in its unit cell, has tensile stability, extreme flexibility, low lattice thermal conductivity, anisotropic Dirac cones, and excellent transparency. So, this material can be a promising candidate in electronics and optics [1,2,3]. We investigate the properties of the valley and spin transport in monolayer borophene. For this purpose, we consider an n-p-n borophene junction of the 8-pmmn type in the presence of a gate voltage (as a potential barrier) and an exchange magnetic field, applied through a ferromagnetic substrate. Using the Hamiltonian of the borophene and using coding in MATLAB software, we plotted the transmission probability and valley and spin polarization versus the Fermi energy of the electron and width of the potential barrier. The effects of transverse wave vector, width, and size of potential barrier on the valley and spin transport are investigated. Applying the gate voltage causes the valley to split. This is one of the advantages of borophene monolayer compared to graphene monolayer because in graphene it is necessary to apply strain in the system to valley splitting. Also, applying an exchange magnetic field causes spin splitting and the generation of spin polarization in the transmitted electron throughout the system. By increasing the width of the potential barrier to values higher than 45 nm, fully spin and valley polarization occurs in the system. As another result, we can control the valley and spin polarization by changing the Fermi energy or size of the potential barrier. Moreover, it can be seen enhancement of the transverse wave vector increases intervals of Fermi energy with fully spin polarization. The mentioned results show that the borophene monolayer has suitable potential for use in spintronic and valleytronic devices and can be beneficial as a valley and spin filter.