Dynamics of Heavy Carriers in the Ferromagnetic Superconductor UGe2

Superconductivity and ferromagnetism in a number of uranium-based materials come from the same f -electrons with a relatively large effective mass, suggesting the presence of a band of heavy quasiparticles, whose nature is still a mystery. Here, UGe 2 dynamics in both ferromagnetic and paramagnetic phases is studied employing high-field μ + SR spectroscopy. The spectra exhibit a doublet structure characteristic to formation of subnanometer-sized magnetic polarons. This model is thoroughly explored here and correlated with the unconventional physics of UGe 2 . The heavy-fermion behavior is ascribed to magnetic polarons; when coherent they form a narrow band, thus reconciling heavy carriers with superconductivity and itinerant ferromagnetism.