Evidence of Haldane-Chain Physics in an Fe-Dehydroindigo Coordination Polymer

RESUMO

We investigate whether an Fe--dehydroindigo coordination polymer can support Haldane-chain physics in its intrinsic, substrate-free limit. Spin-orbit-coupled density-functional-theory calculations and magnetic energy mapping yield a nearly isotropic antiferromagnetic coupling, together with much weaker single-ion anisotropy. Using these parameters, exact diagonalization and density-matrix renormalization group calculations give a nondegenerate ground state separated from the lowest triplet-derived excitations by a gap of about $13$--$14$~meV, on the scale expected for the spin-1 Haldane gap. The anisotropy produces only a small splitting of the low-energy modes. The dynamical spin structure factor places the lowest spectral weight near the antiferromagnetic wave vector $q=\pi$. These results identify the isolated cis-dehydroindigo chain as a material-specific coordination-polymer platform whose microscopic interactions place it in a gapped regime consistent with Haldane-chain physics.