Quantum corrections to the conductivity in a perovskite oxide: a low-temperature study of LaNi_1−xCo_xO₃(0≤x≤0.75)

Abstract

In this paper we propose to study the evolution of the quantum corrections to the conductivity in an oxide system as we approach the metal-insulator (M-I) transition from the metallic side. We report here the measurement of the low-temperature (0.1 K<T<100 K) electrical conductivity of the perovskite-structure oxide system LaNi_1−x Co_xO₃ (0≤x≤0.75). LaNiO₃ is a metal and LaCoO₃ is an insulator. The system is metallic for x≤0.65. For all x, at low temperatures, the conductivity (σ) rises with temperature (T). Below 2 K, σ follows a power-law behavior, σ(T)=σ(0)+αT^m. For samples in the metallic regime, away from the metal-insulator transition (x≤0.4), m≊0.3-0.4. As the transition is approached [i.e., σ(0)→0], m increases rapidly; and at the transition [σ(0)=0, x_c≊0.65], m≊1. On the insulating side (x>0.65), m takes on large values and σ(0)=0. We explain the temperature dependence of σ(T), for T<2 K, on the metallic side (x≤0.4), as arising predominantly from electron-electron interactions, taking into account the diffusion-channel contribution (which gives m=0.5) as well as the Cooper-channel contribution. In this regime, the correction to conductivity, δσ(T), is a small fraction of σ(T). However, as the M-I transition is approached (x→x_c), δσ(T) starts to dominate σ(T) and the above theories fail to explain the observed σ(T).