van der Waals multiferroic tunnel junctions based on sliding multiferroic layered VSi2N4

Multiferroic tunnel junctions (MFTJs) have attracted considerable attention due to their multifunctional properties, which are valuable for nonvolatile memory devices. The recent advancements in van der Waals (vdW) multiferroic materials, combining ferromagnetic and ferroelectric properties, provide an excellent platform for exploring MFTJs at the atomic scale. In this study, we employ a combination of nonequilibrium Green's function and density functional theory to theoretically investigate the spin-dependent transport properties of vdW MFTJs, which consist of metal electrodes and sliding multiferroic layered ${\mathrm{VSi}}_{2}{\mathrm{N}}_{4}$ barrier layers. Our findings demonstrate that asymmetric $\mathrm{Ag}(111)/\text{bilayer}\text{\ensuremath{-}}{\mathrm{VSi}}_{2}{\mathrm{N}}_{4}/\mathrm{Au}(111)$ MFTJs can exhibit multiple nonvolatile resistance states by manipulating the ferroelectric polarization and magnetization alignment of the bilayer ${\mathrm{VSi}}_{2}{\mathrm{N}}_{4}$, achieving maximum tunneling magnetoresistance (TMR) and tunneling electroresistance (TER) ratios of up to $1.01\ifmmode\times\else\texttimes\fi{}{10}^{5}%$ and 37.3%, respectively. More intriguingly, the TER ratio can be further increased to 448.3% by employing left and right symmetric Au(111) electrodes and trilayer ${\mathrm{VSi}}_{2}{\mathrm{N}}_{4}$ barrier layers. Additionally, we reveal that layered ${\mathrm{VSi}}_{2}{\mathrm{N}}_{4}$ possesses intrinsic multiferroicity with the coexistence of the out of plane ferroelectricity and interlayer A-type antiferromagnetism. Through an analysis of electronic structure and Berry curvature, we elucidate the coupling between ferroelectricity and antiferromagnetism via a ferrovalley, enabling electrically controlled magnetism in the bilayer ${\mathrm{VSi}}_{2}{\mathrm{N}}_{4}$ by interlayer sliding. Our results demonstrate that giant TMR, large TER, and multiferroic coupling can coexist in layered ${\mathrm{VSi}}_{2}{\mathrm{N}}_{4}$, with potential applications in other vdW layered multiferroics. The controllable interlayer sliding of vdW MFTJs offers promising opportunities for the design of next-generation logic and memory devices.