Nematic heavy fermions and chiral magnetic phases in CeSiI

The recently discovered van der Waals material CeSiI exhibits properties including heavy quasiparticle behavior and spiral order with strong magnetic anisotropy, making it a potential host for topological spin textures such as skyrmions. Its unique monolayer structure consists of two layers of Ce atoms on triangular lattices sandwiching a silicene layer, with Ce sites located at the center of the honeycomb lattice. This arrangement results in an effective extended Kondo interaction along with a predominant ferromagnetic RKKY interaction. Via mean-field theory of Abrikosov fermions, our analysis indicates that the ground state of the monolayer can exhibit a non-magnetic nematic heavy fermion phase that breaks C6 rotational symmetry for small Heisenberg exchange, while for larger values we observe a magnetically ordered phase and a coexistence of magnetic order and uniform heavy Fermi liquid on separate Ce layers, depending on the strength of the Heisenberg exchange. In the magnetic phase, we explore the magnetic phase diagram as a function of anisotropy and applied magnetic field using an effective spin model. Notably, an external electric field can allow for fine-tuning of intra- and interlayer magnetic couplings, potentially stabilizing a novel vortex phase. These findings highlight the unique advantages and tunability of van der Waals heavy fermion materials for manipulating chiral magnetic phases and exploring unconventional quantum states.