Jörn Venderbos1
Drexel University1
The family of layered transition-metal trichalcogenides (MPX3) has recently attracted much attention as a versatile platform for exploring magnetism in van der Waals materials, and offer a potential venue for realizing intrisinc two-dimensional magnetism. This talk will discuss the magnetic phases observed in these honeycomb magnets, highlighting in particular the accidental degeneracy of classical ground states in a frustrated honeycomb lattice Heisenberg model. Fluctuations lift this degeneracy via the order-by-disorder mechanism, which is demonstrated by developing a systematic spin wave theory. As a result of the accidental degeneracy at the classical level, linear spin wave theory is insufficient to accurately describe the spin wave dispersion---an experimentally relevant characterstic. Indeed, at the quadratic level pseudo-Goldstone modes are present, which are gapped by higher order quantum corrections. This talk will further address the nature of the quantum phase transition between a paramagnet and a rotation symmetry broken ordered state of the kind observed in some members of MPX3 family. In particilar, this talk will show that this transition can proceed in two steps, with the rotation symmetry broken first as the ordered state is approached, thus giving rise to a Potts-nematic phase.