Ground State in artificial square ice

Thermal ground-state ordering and elementary excitations in artificial magnetic square ice.
Jason P. Morgan, Aaron Stein, Sean Langridge, Christopher H. Marrows
Nature Physics 7, 68 (2011)

a, Direct observation of frozen-in long-range GS order with ~10-μm-width domains, separated by antiferromagnet-like DW boundaries, supporting localized elementary excitations of small groups of moments flipped against the background. A magnified region, containing a DW and localized excitations (1, 2L, 3Z, notation explained in the text), is shown in the inset. A key identifying the rotationally degenerate vertex configurations is also shown. The green square indicates a large domain-like excitation. b, Moment arrangements of the regions highlighted in a, indicating the flipped elements (grey), T₂-dipole (green arrow) and T₃-monopole vertices (red and blue circles) making up the defects.