Structure of the nearly-degenerate manifold of lattice quasiholes on a torus

Abstract: We study the nearly-degenerate quasihole manifold of the bosonic Hofstadter-Hubbard model on a torus, known to host the lattice analog of the Laughlin state at filling fraction $\nu = 1/2$. Away from $\nu = 1/2$ and in the presence of both localized and delocalized quasiholes, the ratio between the numerically calculated many-body Chern number for certain groups of states and the number of states in the relevant group turns out to be constant for this manifold, which is also manifested in the density profile as the depleted charge of localized quasiholes. Inspired by a zero-mode counting formula derivable from a generalized Pauli principle, we employ a combinatorial scheme to account for the splittings in the manifold, allowing us to interpret some groups of states as the quasihole excitations corresponding to filling fractions lower than $\nu = 1/2$. In this scheme, the many-body Chern number of subgroups appears as a simple combinatorial factor.