Pseudopotential Formalism for Fractional Chern Insulators

TL;DR

This paper develops a pseudopotential formalism for fractional Chern insulators using Wannier functions, enabling systematic analysis of interactions and ground states, and addressing inhomogeneous Berry curvature effects.

Contribution

It introduces a pseudopotential Hamiltonian framework for fractional Chern insulators based on Wannier functions, extending FQH concepts to lattice models.

Findings

Defined a set of two-body pseudopotential Hamiltonians with magnetic translation symmetry.

Compared pseudopotential expansions across different fractional Chern insulator models.

Discussed the impact of inhomogeneous Berry curvature on Hamiltonian expansion and low-energy theories.

Abstract

Recently, generalizations of fractional quantum Hall (FQH) states known as fractional quantum anomalous Hall or, equivalently, fractional Chern insulators states have been realized in lattice models. Ideal wavefunctions such as the Laughlin wavefunction, as well as the corresponding trial Hamiltonians for which the former are exact ground states, have been vital to characterizing FQH phases. The Wannier function representation of fractional Chern insulators proposed in [X.-L. Qi, Phys. Rev. Lett., 126803] defines an approach to generalize these concepts to fractional Chern insulators. In this paper, we apply the Wannier function representation to develop a systematic pseudopotential formalism for fractional Chern insulators. The family of pseudopotential Hamiltonians is defined as the set of projectors onto asymptotic relative angular momentum components which forms an orthogonal basis of two-body Hamiltonians with magnetic translation symmetry. This approach serves both as an expansion tool for interactions and as a definition of positive semidefinite Hamiltonians for which the ideal fractional Chern insulator wavefunctions are exact nullspace modes. We compare the short-range two-body pseudopotential expansion of various fractional Chern insulator models at one-third filling in phase regimes where a Laughlin-type ground state is expected to be realized. We also discuss the effect of inhomogeneous Berry curvature which leads to components of the Hamiltonian that cannot be expanded into pseudopotentials, and elaborate on their role in determining low energy theories for fractional Chern insulators. Finally, we generalize our Chern pseudopotential approach to interactions involving more than two bodies with the goal of facilitating the identification of non-Abelian fractional Chern insulators.