2025/11/11 by Mauri, Achille, Roose, Siebe, Mila, Frédéric · 1 citation
#FOS: Physical sciences #Strongly Correlated Electrons (cond-mat.str-el)
paper · doi:10.48550/arxiv.2511.08179
Motivated by recent experimental studies, we investigate the spectrum of the nearest-neighbour triangular XXZ model within the 1/S expansion, in the limit in which the exchange couplings present a strong easy-axis anisotropy Jxy/Jzz ≪ 1. We show that in the limit in which 1/S → 0 and Jxy → 0 at fixed V = Jzz/(S Jxy), the triangular spin model can be reduced to an effective boson model with quartic interactions on the honeycomb lattice. This effective model interpolates between a spin-wave (V → 0) and a strong-coupling limit (V → ∞), and encodes in a simple framework the regimes discussed by Kleine et al. [Z. Phys. B Condens. Matter 86, 405 (1992); 87, 103 (1992)]. For zero field, the classical ground state of the model presents an accidental degeneracy, which has a particularly simple form and which can be expressed in terms of a simple symmetry of the classical energy. The model thus offers a particularly transparent realization of a theory with quantum order-by-disorder and a pseudo-Goldstone mode. We analyze the spectrum at zero magnetic field by calculating the self-energy at one-loop order, using a self-consistent renormalization of the gap and the energy scale. Within the self-consistent approximation considered here, the corrections present a complex evolution as a function of V. We discuss the one-loop corrections in comparison with the spectrum observed experimentally in K2Co(SeO3)2.