Impact of gapped spin-orbit excitons on low energy pseudospin exchange interactions

Abstract

The quest for exotic quantum magnetic ground states, including the Kitaev spin liquid and quantum spin-ices, has led to the discovery of several quantum materials where low energy pseudospin-1/2 doublets arise from the splitting of spin-orbit entangled multiplets with higher degeneracy. Such systems include d-orbital and f -orbital Mott insulators. When the gap between the low energy pseudospin-1/2 levels and the excited levels of the multiplet or 'excitons' is not large, the effective low-energy exchange interactions between the low energy pseudospin-1/2 moments can acquire significant corrections from coupling to the excitons. We extract these corrections using higher order perturbation theory as well as an exact Schrieffer-Wolff transformation. Such corrections can impact the exchange matrix for the low energy pseudospin-1/2 levels by renormalizing the strength and the sign of Heisenberg exchange or Ising anisotropies, and potentially even inducing bond-anisotropic couplings such as Kitaev-Γ exchange interactions. We discuss recent experiments on various cobaltate and osmate materials which hint at the ubiquity and importance of this physics.

The Shanghai alliance of multilingual researchers: Fudan University, Tongji University, Shanghai University of Finance and Economics, and Shanghai International Studies University, China

“…Since crystal electric field (CEF) interactions play a vital role in determining both the magnetic ground state and single-ion anisotropy of rare-earth ions [19][20][21], it is essential to uncover the CEF spectra in order to understand the exotic quantum states found in triangular-lattice magnets. In addition to determining the CEF parameters and eigenvalues, measuring the dis-In the last few years, a new class of triangular-lattice antiferromagnet ARCh 2 (A = alkali or monovalent ion, R = rare earth, Ch = chalcogen) has attracted great attentions due to its potential in realizing novel quantum states [27].…”

Interplay between crystal field and magnetic anisotropy in the triangular-lattice antiferromagnet NaTmTe2

“…Unlike TmMgGaO 4 [15,16] and KTmSe 2 [17], the magnetic anisotropy observed in NaTmTe 2 notably deviates from Ising behavior, suggesting the presence of a distinct CEF ground state in NaTmTe 2 [27,28]. To gain insights into the CEF structure and spin exchange parameters, we conducted neutron scattering measurements to unveil the magnetic excitation spectra.…”