Valley- and Orbital-Controlled 2D Chern Insulators Without Spin-orbit Interaction

Abstract

We present a theoretical study of orbital-induced topological phase transitions in a two-dimensional lattice model with staggered potential $(\Delta)$ and orbital coupling $(\lambda)$ competing with the hopping strength. By tuning these parameters, two gap-closing mechanisms emerge: valley closure at $\mathbf{K}$ and $\mathbf{K'}$ for $\lambda=\pm\Delta$, and a $\mathbf{\Gamma}$-point closure at $\lambda=\pm\sqrt{\Delta^2+9t_0^{2}}$. Their interplay defines a topological window in which the Berry curvature localizes near a single valley, yielding a quantized anomalous Hall conductivity ($\sigma_{xy}=e^{2}/h$) and Chern number ($C=1$). These results demonstrate orbital-driven Chern insulating behavior without spin-orbit coupling. The resulting phase diagram captures the transition from trivial to topological phases and suggests practical routes for orbital engineering in tunable lattice systems.