Artificial spin ices (ASIs) are interacting arrays of lithographically defined nanomagnets in which novel, frustrated magnetic phases can be intentionally designed. A key emergent description of fundamental excitations in ASIs is that of magnetic monopoles - mobile quasiparticles that carry an effective magnetic charge. Here, we demonstrate that the archetypal square ASI lattice can host, in specific regions of its magnetic phase diagram, plasmalike regimes containing a high density of mobile magnetic monopoles. These regimes result from the magnetic field-tunable tension on the Dirac strings connecting mobile monopoles. By passively "listening"to spontaneous monopole noise under conditions of strict thermal equilibrium, we reveal their intrinsic dynamics and show that monopole kinetics are most diffusive (that is, minimally correlated) in the plasma regime. These results open the door to on-demand monopole regimes having continuously field-tunable densities and dynamic properties, thereby providing a new paradigm for probing the physics of effective magnetic charges in synthetic matter.
Bibliographical noteFunding Information:
We gratefully acknowledge support from the Los Alamos Laboratory Directed Research and Development (LDRD) program and discussions with Clare Yu, Herve Carruzzo, and Gia-Wei Chern. Work at the National High Magnetic Field Lab was supported by the National Science Foundation (NSF) Grant No. DMR-1644779, the State of Florida, and the U.S. Department of Energy. Work at Yale University was funded by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under Grants No. DE-SC0010778 and No. DE-SC0020162. Work at the University of Minnesota was supported by the NSF through Grant No. DMR-1807124.
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