We study artificial spin ice with isolated elongated nanoscale islands arranged in a kagome lattice and solely interacting via long range dipolar fields. The artificial kagome spin ice displays a phenomenology similar to the microscopic pyrochlore system, where excitations at sub-Kelvin temperatures consist of emergent monopole quasiparticles that are connected via a solenoidal flux line, a classical and observable version of the Dirac string. We show that magnetization reversal in kagome spin ice is fundamentally different from the nucleation and extensive domain growth scenario expected for a generic 2D system. Here, the magnetization reverses in a strictly ID fashion: After nucleation, a monopole-antimonopole dissociates along a ID path, leaving a (Dirac) string of islands with reversed magnetization in its wake. Since the 2D artificial spin ice spontaneously decays into a ID subsystem, magnetization reversal in kagome spin ice provides an example of dimensional reduction via frustration.
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