Electronic correlation across the metal-insulator transition in single crystals of β-Na_0.33V₂O₅

The Wadsley-type vanadium bronze β-Na_0.33V₂O₅ exhibits a thermally driven metal-insulator transition (MIT) due to charge ordering at T_CO = 136 K. This type of correlated behavior is typically observed in these β(β’)-vanadium bronzes and are induced by the local lattice distortions and electrical interactions due to the intercalated dopants as they sit within the tunnel structure formed by chains of V₂O₅. The evolution of the thermally driven MIT in single crystals of β-Na_0.33V₂O₅ using electrical transport and noise spectroscopy measurements is studied to elucidate the charge dynamics across this transition. We observe a crossover from an Arrhenius-type conductivity above T_CO to a Mott variable range hopping. This crossover can alternately be observed in the power spectral density (PSD) of the residual resistance fluctuations as a gradual change in the noise magnitude as charges localize and order in the insulating state. The slope of the PSD also deviates significantly signifying a mixing of phases as we transition from a charge disordered to an ordered state. Vanadium bronzes prove to be fertile playgrounds to understand tunable correlated electron behavior in nanoscale systems.