Excitonic Magnetism in Van Vleck-type d~4 Mott Insulators

摘要

In Mott insulators with the t~4_(2g） electronic configuration such as of Re~(3+), Ru~(4+), Os~(4+), and Ir~(5+) ions, spin-orbit coupling dictates a Van Vleck-type nonmagnetic ground state with an angular momentum J = 0, and the magnetic response is governed by gapped singlet-triplet excitations. We derive the exchange interactions between these excitons and study their collective behavior on different lattices. In perovskites, a conventional Bose condensation of excitons into a magnetic state is found, while an unexpected one-dimensional behavior supporting spin-liquid states emerges in honeycomb lattices, due to the bond directional nature of exciton interactions in the case of 90° d-p-d bonding geometry.