An introduction to hydrodynamic spin lattices

This article is an introduction for non-specialist readers to hydrodynamic spin lattices, collections of macroscopic wave-propelled particles that exhibit symmetry-breaking phenomena. Hydrodynamic spin lattices have been introduced and thoroughly investigated with both experiments and theoretical models by Sáenz et al. (Nature, 596 (2021) 58). Here I summarize the main results obtained in experiments with one-dimensional lattices and describe the simplest theoretical model, i.e., the generalized Kuramoto model, that captures the experimental data. The results presented here include transitions from antiferromagnetic to ferromagnetic order obtained by varying lattice geometry and system rotation, which is equivalent to applying a magnetic field. Finally, hydrodynamic spin lattices are briefly discussed in the context of active systems.