Semiclassical Band Splitting in the Infinite Chern Band Model

Abstract: We study the two lowest Bloch bands of the infinite Chern band model in the semiclassical limit. When the Berry curvature parameter is an odd multiple of (π), we derive an explicit asymptotic formula for their exponentially small splitting, uniformly over the Brillouin torus. The proof combines Agmon estimates and WKB approximations for a matrix Schrödinger operator whose lowest potential eigenvalue has two wells. Geometric properties of the Agmon distance allow us to compute the leading tunneling coefficients by the method of stationary phase. We provide numerical computations to illustrate the asymptotic formula and support the conjecture that the two bands remain separated for other values of the Berry curvature parameter.