Colloquia

Since Phil Anderson's "More is Different" or perhaps since Landau's conceptualization of quantum liquids, condensed matter physicists have modeled the emergent behavior of complex matter by boiling it down to the relevant emergent degrees of freedom, symmetries and interaction. What if we could invert that approach? Instead of developing Hamiltonians that conceptualize unusual phenomena seen in materials found serendipitously in nature, we could create artificial materials deliberately for exotic emergent behaviors. That was the perhaps ambitious goal of artificial spin ices (arrays of interacting, magnetic frustrated nano-islands representing binary magnetic variables) since its inception in 2006. Since then, advances in fabrication and characterization have allowed to push that envelope to show magnetic monopoles, ordering of magnetic charges, and a wealth of emergent phenomena. We shall discuss two of the most recent results: a system that orders by raising its entropy [1] and another one showing a topological crossover in its kinetics [2].

[1] SAGLAM, Hilal, et al. Entropy-driven order in an array of nanomagnets. Nature Physics, 2022, 18.6: 706-712.

[2] ZHANG, Xiaoyu, et al. Topological kinetic crossover in a nanomagnet array. Science, 2023, 380.6644: 526-531.