Abstract
Electric charge screening is a fundamental principle governing the behaviour in a variety of systems in nature. Through reconfiguration of the local environment, the Coulomb attraction between electric charges is decreased, leading, for example, to the creation of polaron states in solids or hydration shells around proteins in water. Here, we directly visualize the real-time creation and decay of screened magnetic charge configurations in a two-dimensional artificial spin ice system, the dipolar dice lattice. By comparing the temperature dependent occurrence of screened and unscreened emergent magnetic charge defects, we determine that screened magnetic charges are indeed a result of local energy reduction and appear as a transient minimum energy state before the system relaxes towards the predicted ground state. These results highlight the important role of emergent magnetic charges in artificial spin ice, giving rise to screened charge excitations and the emergence of exotic low-temperature configurations.
Highlights
Electric charge screening is a fundamental principle governing the behaviour in a variety of systems in nature
The formation of simple ferro- or anti-ferromagnetic configurations is prevented, which leads to the emergence of new phases that cannot be described in a conventional manner, such as the infamous spin ice phase in magnetic pyrochlore materials[1], which was successfully described using the concept of emergent magnetic charges[4]
The most recent emergence of artificial spin ices with thermally activated moment fluctuations[5,6,9,10,12] delivered evidence on the important role of emergent magnetic charge defects in thermal relaxation processes[6,10], and that screening effects between emergent magnetic charges are crucial for charge-ordering phenomena in a two-dimensional shakti lattice[15] and the possible emergence of polaronic states in artificial spin ice[16]
Summary
Electric charge screening is a fundamental principle governing the behaviour in a variety of systems in nature. The most recent emergence of artificial spin ices with thermally activated moment fluctuations[5,6,9,10,12] delivered evidence on the important role of emergent magnetic charge defects in thermal relaxation processes[6,10], and that screening effects between emergent magnetic charges are crucial for charge-ordering phenomena in a two-dimensional shakti lattice[15] and the possible emergence of polaronic states in artificial spin ice[16] This raises the question, whether these emergent magnetic charge screening phenomena are just a result of the lattice geometry or originate from a minimization of interaction energies between the involved entities. Analysing the low-temperature configurations achieved after cooling the sample from 350 to 140 K (Fig. 2a–f), we find for all lattice spacings that the zero-charge V1 vertex types dominate at z6 vertices (Fig. 2g), while z3 vertices show a clear tendency a
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