Anomalous temperature behavior of resistivity in lightly doped manganites around a metal-insulator phase transition

TL;DR

This study investigates the unusual temperature-dependent resistivity behavior in lightly Cu-doped manganites near a metal-insulator transition, revealing complex peak splitting and proposing a tunneling conductivity explanation.

Contribution

It reports the first observation of resistivity peak splitting in lightly doped manganites and models this behavior with a nonthermal tunneling conductivity framework.

Findings

Resistivity peak splits into two with Cu doping.

The second peak's behavior changes at a critical doping level.

Data fits well with a tunneling conductivity model.

Abstract

An unusual temperature and concentration behavior of resistivity in $La_{0.7}Ca_{0.3}Mn_{1-x}Cu_xO_3$ has been observed at slight $Cu$ doping ($0\leq x \leq 0.05$). Namely, introduction of copper results in a splitting of the resistivity maximum around a metal-insulator transition temperature $T_0(x)$ into two differently evolving peaks. Unlike the original $Cu$-free maximum which steadily increases with doping, the second (satellite) peak remains virtually unchanged for $x<x_c$, increases for $x\ge x_c$ and finally disappears at $x_m\simeq 2x_c$ with $x_c\simeq 0.03$. The observed phenomenon is thought to arise from competition between substitution induced strengthening of potential barriers (which hamper the charge hopping between neighboring $Mn$ sites) and weakening of carrier's kinetic energy. The data are well fitted assuming a nonthermal tunneling conductivity theory with randomly distributed hopping sites.