We demonstrate that a spin degree of freedom can introduce additional texture to higher order topological insulators (HOTIs), manifesting itself in novel topological invariants, phases, and phase transitions. Spin-polarized mid-gap corner states of various multiplicities are predicted for different HOTI phases, and novel bulk-boundary correspondence principles are defined based on quantized bulk invariants such as total and spin corner charge. Those are shown to be robust with respect to symmetry-preserving spin-flipping perturbations. Photonic realizations of spin-linked topological phases are demonstrated in engineered systems with synthetically emulated spin degree of freedom.
@article{arxiv.2102.12944,
title = {Spin-Polarized Fractional Corner Charges and Their Photonic Realization},
author = {Ran Gladstein Gladstone and Minwoo Jung and Gennady Shvets},
journal= {arXiv preprint arXiv:2102.12944},
year = {2022}
}