Effective field theory for anisotropic antiferromagnets: Gapped Goldstone bosons, pseudo-Goldstone excitations, and phase transitions
Phys. Rev. B 112, 064408 – Published 5 August, 2025
DOI: https://doi.org/10.1103/msy3-ztxr
Abstract
We build and discuss a low energy effective field theory for anisotropic antiferromagnets in the presence of an external magnetic field. Such an effective theory is simple yet rich and features a number of phenomena such as the appearance of gapped Goldstones, pseudo-Goldstones, and a first order “spin flop” phase transition, all within the regime of validity of the theory. We also discuss in detail, the quantization procedure of the free theory in the presence of a magnetic field, which is made nontrivial by the presence of a single-time derivative term. This class of materials makes a precious test field for exotic phenomena in quantum field theory. Moreover, we explicitly perform the matching of the effective theory to the short distance theory of a specific antiferromagnet, namely, nickel oxide. The latter is particularly relevant in light of recent proposals of employing this material towards the hunt for light dark matter. As a byproduct of our study, we also re-evaluate the role played by discrete symmetries in magnetic materials, presenting it in a way that is completely consistent with the proper low energy EFT ideology.
