Spontaneous Valley Polarization in Two-Dimensional Ferro-valley V_xNb_4−xSe₈ (X=1, 2, 3) Alloy for Valleytronic and Spintronic Devices Using First Principle Calculations

Two-dimensional ferro-valley materials have garnered significant research interest due to their inherent valley polarization, which holds potential usage in valley-based nonvolatile RAM and valley filters. In this research work, the electronic and magnetic properties of the two-dimensional novel ferro-valley alloy $\mathbf{V}_{x} \mathbf{N b}_{4-x} \mathbf{S e}_{8}$ have been explored for the first time. Density functional theory is employed within the framework of first-principles calculations to achieve this. The electronic band structure was computed with and without spin-orbit coupling (SOC), demonstrating substantial alterations in the band dispersion due to SOC effects. This investigation predicts that the alloys are a bipolar magnetic semiconductor having an indirect bandgap. Magnetization energy calculations show that the ferromagnetic (FM) state is more favourable than the antiferromagnetic (AFM) state, indicating a robust ferro-valley behavior. Lack of inversion symmetry and time reversal symmetry causes spontaneous valley polarization in these materials without the application of any external factor, which was found to be $105.1 \mathrm{meV}, 139.1 \mathrm{meV}$, and 189.9 meV at the valence band for $\mathrm{V}_{3} \mathrm{NbSe}_{8}, \mathrm{~V}_{2} \mathrm{Nb}_{2} \mathrm{Se}_{8}$ and VNb<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Se<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</inf>, respectively. For the conduction band, the valley splitting energy is found to be $42.4 \mathrm{meV}, 85.6 \mathrm{meV}$, and 45 meV, respectively. Valley Degree of Freedom (DOF) and their manipulation can lead to quantum information processing and logic applications. Furthermore, these materials are spin filter materials exhibiting distinct bandgap for up-spin and down-spin electrons. Due to this, selective transport of up-spin and down-spin electrons is attainable, rendering them appropriate for spin filter devices. Owing to their inherent valley polarization and spin filtering properties, these materials are appropriate for valleytronic and spintronic applications.