Gating dynamics in ionic-liquid-gated FeS₂ single crystals

Ionic liquid (IL) gating has proven remarkably effective in voltage control of superconductivity, insulator-metal transitions, and magnetism. This is in large part due to its high electric fields, and thus large accumulated surface charge densities (> 10¹⁴ cm^-2). Recent studies, however, emphasize the importance of distinguishing electrostatic from electrochemical gating mechanisms in such devices. Here, we present a detailed study of the transport dynamics of IL-gated FeS₂ single crystals, where a positive gate voltage is observed to induce a remarkable insulator-metal and diamagnetic-ferromagnetic transition. This transition is found to be highly reversible in transport, which, given the delicate nature of surface conduction in FeS₂ [1], strongly evidences an electrostatic gating mechanism. Hysteretic gate voltage sweeps suggest the electrostatic electron accumulation and depletion to be spatially non-uniform, with a sweep-direction-dependent percolation transition. The observation of reversible electrostatic response is discussed in terms of the formation enthalpy and diffusivity of S vacancies in FeS₂.
[1] Walter et al., Phys. Rev. Materials, 1, 065403 (2017).