Pseudomagnetic fields, particle-hole asymmetry, and microscopic effective continuum Hamiltonians of twisted bilayer graphene
Jian Kang, Oskar Vafek
Abstract
Using the method developed in the companion paper [O. Vafek and J. Kang, Continuum effective Hamiltonian for graphene bilayers for an arbitrary smooth lattice deformation from microscopic theories, Phys. Rev. B 107, 075123 (2023)], we construct effective continuum theories for two different microscopic tight-binding models of twisted bilayer graphene at a twist angle of $1.{05}^{\ensuremath{\circ}}$, one Slater-Koster based and the other ab initio Wannier based. The energy spectra obtained from the continuum theory---either for rigid twist or including lattice relaxation---are found to be in nearly perfect agreement with the spectra from tight-binding models when the gradient expansion is carried out to second order, demonstrating the validity of the method. We also analyze the properties of the Bloch states of the resulting narrow bands, finding non-negligible particle-hole symmetry breaking near the $\mathrm{\ensuremath{\Gamma}}$ point in our continuum theory constructed for the ab initio-based microscopic model due to a term in the continuum theory that was previously overlooked. This reveals the difference with all existing continuum models where the particle-hole symmetry of the narrow band Hilbert space is nearly perfect.