Exact eigenvalues and experimental signatures of Heisenberg-Kitaev interactions in spin-1/2 quantum clusters

Abstract: We investigate the thermodynamics and energy eigenstates of a spin-1/2 coupled trimer, tetramer in a star configuration, and tetrahedron. Using a Heisenberg Hamiltonian with additional Kitaev interactions, we explore the thermodynamic signatures of the Kitaev interaction. Our results show that introducing a Kitaev interaction generates a second Schottky anomaly in the heat capacity for systems with a large K/J ratio. The Kitaev term also introduces nonlinear eigenvalues with respect to a magnetic field, pushing the clusters toward a regime similar to the incomplete Paschen-Back effect and triggering first and second-order quantum phase transitions along with robust thermodynamic behavior. Through this approach, we provide exact analytical solutions that offer insights into Kitaev interactions, both in molecular magnets and in extended systems such as honeycomb or Kagome lattices. Furthermore, we provide insight into experimental measurements for detecting Kitaev interactions in clusters.