Going Beyond the Ising Model in Co-based S=1/2 Quantum Chains

The one-dimensional (1D) transverse-field Ising model is one of the simplest systems with a quantum critical point, and Cobalt-based S=1/2 chains stand out as thoroughly studied realizations of such model. One recent example is the compound BaCo₂V₂O₈ which, despite its Ising-like characteristics, possesses unusual field-dependence, modeled by a site-dependent g-tensor. This has been proposed to lead to a topological transition at the critical field. In this talk, I will present a microscopic theory of the nearest-neighbor spin-exchange interactions in this material that goes beyond the current model. I will show that on top of the conventional Heisenberg exchange, a strong Kitaev interaction as well as a small Gamma interaction, both bond-dependent, emerge. I will explore how these interactions are responsible for the observed behavior, and how it gives rise to rich phenomena beyond what is found in the current description.