From ionic insulator to filamentary correlated metal: Non-Fermi-liquid behavior in CuCl

Abstract

The ionic insulator copper chloride CuCl undergoes a dramatic electric-field-induced transition to a correlated metallic state, exhibiting striking non-Fermi-liquid (NFL) behavior. We demonstrate that a 70 V bias applied to compressed CuCl pellets triggers resistive switching from highly insulating 106 Ω to metallic 103 Ω states at room temperature, accompanied by characteristic non-linear I–V curves showing (i) hysteresis upon cycling and (ii) a 33 V threshold for electronic reordering. This transition is attributed to metallic copper filament formation via solid-state electrolysis, creating a heterogeneous system where the I–V evolution confirms competing processes: filament growth (ohmic → metallic) and oxidative degradation (non-linear → insulating). Temperature-dependent resistance in the metallic state reveals anomalous power-law behavior (R ∼ Tα, α = 1.2–2.1), deviating from Fermi-liquid expectations (α = 2). Magnetoresistance shows a crossover from negative (T < 60 K) to positive (T > 60 K) regimes, indicating competition between weak localization and spin scattering. Oxidation to Cu2Cl(OH)3 introduces magnetic interactions that further modulate transport. The I–V characteristics' dependence on cycling and threshold voltages establishes CuCl as a tunable platform for NFL phenomena, bridging ionic insulators and correlated conductors through electrochemically gated filamentary networks.