Localised-hopping to extended-state transport: Investigating the insulator to metal transition in vacancy doped SmN

The magnetic properties of the rare-earth nitride series are determined largely by the occupation of the 4f electron shell [1]. However, in a select few members, the localized 4f states hybridize with the extended 5d states at the Fermi energy and thus also directly influence electrical transport [2-5]. Here we discuss a combined experimental and computational study of nitrogen-vacancy doped SmN. We show that the material crosses an insulator-to-metal transition as samples are increasingly doped with nitrogen vacancies (Figure 1). At low doping levels, the transport can be understood as variable range hopping between defect states, while at high doping levels extended state metallic transport is seen. In the intermediary 'anomalous metallic' region where transport is in a mixed 4f-5d band, there are indications of more exotic ground states, such as unconventional superconductivity [6], which furthermore may coexist with ferromagnetic order.