Ultra-thin filaments revealed by the dielectric response across the metal-insulator transition in VO2

Temperature dependent dielectric spectroscopy measurements on vanadium dioxide thin films allow us to distinguish between the resistive, capacitive, and inductive contributions to the impedance across the metal-insulator transition (MIT). We developed a single, universal, equivalent circuit model to describe the dielectric behavior above and below the MIT. Our model takes account of phase-coexistence of metallic and insulating regions. We find evidence for the existence at low temperature of ultra-thin threads as described by a resistor-inductor element. A conventional resistor-capacitor element connected in parallel accounts for the insulating phase and the dielectric relaxation.