Spin-orbit entanglement in Mn³⁺ driven by Jahn-Teller distortions

Spin-orbit entanglement in 4d and 5d transition metal systems can enhance electronic correlations, leading to nontrivial ground states and the emergence of exotic excitations. There is also an interest to investigate spin-orbit entanglement in 3d compounds, though this is challenging due to their smaller spin-orbit coupling. Here we analyze multi-orbital 3d transition metals involving t_2g and e_g states interacting with light, offering ways to tune their properties and uncover novel physics. In particular, we discuss how the Jahn-Teller effect in Mn³⁺ lifts the orbital degeneracy in the e_g manifold, reducing the energy gap between high- and low- spin-orbital states, leading to enhanced spin-orbit entanglement [i. ii, iii]. Through magneto-optical spectroscopy we have revealed such strong spin-orbital-lattice coupling, resulting from Jahn-Teller polarons interacting with electromagnetic radiation. To model these light-matter interactions we appliy group-theoretic quantum chemistry methods [ii] and many-body group-theoretical techniques. Our results show a rare example of synergistic effects of Jahn-Teller and spin-orbit interactions and provide a way to entangle different degrees of freedom in d-metal oxides, which may allow paths to explore the interplay of orbital, lattice and spins in 3d correlated systems.

[i]. Casals et al. Phys. Rev. Lett. 117, 026401 (2016).

[ii]. Miñarro & Herranz, Phys. Rev. B 106, 165108 (2022)

[iii]. Miñarro et al. Nat Commun 15, 8694 (2024)