• Accepted Paper

Microsopic theory of spin polarons in Chern ferromagnets

Qiang Gao and Eslam Khalaf

Phys. Rev. Lett. - Accepted 3 November, 2026

DOI: https://doi.org/10.1103/8mtx-9bv4

Abstract

Charged excitations in Chern ferromagnets play a central role in determining the nature of doped phases in moiré heterostructures. We develop a microscopic theory of charged excitations in an SU(2) Chern ferromagnet and obtain closed-form wavefunctions for a hierarchy of charge-e spin polaron states binding an arbitrary number of spin flips. In an ideal Chern-1 band with a normal-ordered contact interaction, we show that these polarons are exact eigenstates of the Hamiltonian with the same energy as single-hole excitations. Away from this ideal limit, we promote these states to a variational family by introducing a single size parameter and (in dispersive Chern bands) a geometry-informed single-particle dressing. Our momentum-space wavefunctions admit two equivalent representations: a ratio of jastrow factors of Weierstrass functions of relative momenta or an antisymmetrized geminal product of particle-hole wavefunctions. The latter enables efficient evaluation of overlaps and expectation values for large system sizes and large number of spin flips. Benchmarking in the lowest Landau level, the single-spin-flip ansatz achieves 99% overlap with exact diagonalization and accurately captures binding energies, while the multi-spin-flip energies interpolate smoothly toward the large-texture (skyrmion) regime. For Chern bands with tunable quantum geometry, we find that interaction-generated single particle dispersion quickly destabilizes the spin polarons once quantum geometry becomes sufficiently nonuniform. When such dispersion is suppressed, however, the bound states persist deeper into the non-uniform regime, with the binding energy slowly decreasing and the bound state becoming larger as the quantum geometry becomes more concentrated. Our results provide a microscopic foundation for analyzing doped Chern ferromagnets in moiré platforms and lay the groundwork for variational wavefunctions of multi-polaron excitations and phases.

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