Designing Hamiltonians with Exactly Flat Higher-Vortexable Bands

Abstract

The zero modes of the Aharonov-Casher Hamiltonian form an exactly flat, vortexable Chern band in any nonuniform magnetic field, analogous to the lowest Landau level. We ask which local Hamiltonians host exactly flat higher-vortexable bands. For a scalar Hamiltonian, an exactly flat first-vortexable band requires a mass proportional to the local field; the Dirac analogue has the same structure. For periodic Bernal bilayer graphene with nonzero mean flux, the exact zero-mode pair is genuinely first-vortexable if and only if the interlayer hopping has nonzero mean; zero-mean hopping instead gives a decomposable pair. Multiorbital models yield exact higher-vortexable chains to arbitrary order, while remaining first order in momentum.