Speaker
Description
Rare-earth triangular-lattice compounds stand as prime candidates for harboring exotic quantum spin liquid (QSL) phases, but their effective low-energy Hamiltonians and magnetic ground states remain difficult to determine experimentally. We evaluate ab initio effective spin-1/2 Hamiltonians for a set of Ce and Yb triangular lattice compounds from their paramagnetic electronic structure using the force theorem in Hubbard-I method. This force-theorem approach is generalised to include, apart from 4$f$ kinetic exchange, also indirect exchange induced through the 4$f$-5$d$ on-site Coulomb interaction. The resulting Hamiltonians are solved using either single-site quantum mean-field or exact diagonalization of finite-size clusters. For the triangular lattice Ce delafossites CsCeSe$_2$, KCeS$_2$, and RbCeO$_2$, we find that the indirect exchange dominates in the selenide, the kinetic exchange in the oxide, while both mechanisms contribute almost equally in the sulfide. Overall, we find conventional ordered magnetic ground states for all studied compounds, including some putative QSL candidates. Our findings highlight a possibly important role of deviations from the perfect triangular model—like atomic disorder—in real triangular-lattice materials.
[1] L. V. Pourovskii, R. Soares, A. Wietek, Phys. Rev. B 113, L060401 (2026).
[2] L. V. Pourovskii, arXiv:2511.14904.