High Temperature Thermopower in La_{2/3}Ca_{1/3}MnO_3 Films: Evidence for Polaronic Transport

TL;DR

This study investigates high-temperature thermopower in La_{2/3}Ca_{1/3}MnO_3 films, providing evidence for polaronic conduction mechanisms in colossal magnetoresistance materials through various experimental measurements.

Contribution

It presents experimental evidence for polaron-dominated conduction in CMR materials, highlighting high-temperature thermopower behavior and magnetic polarization of polarons.

Findings

Large, field-independent difference between activation energies for resistivity and thermopower at high T

ln(rho) does not scale with magnetization near T_c

Thermopower follows a 1/rho law below T_c

Abstract

Thermoelectric power, electrical resistivity and magnetization experiments, performed in the paramagnetic phase of La_{2/3}Ca_{1/3}MnO_3, provide evidence for polaron-dominated conduction in CMR materials. At high temperatures, a large, nearly field-independent difference between the activation energies for resistivity (rho) and thermopower (S), a characteristic of Holstein Polarons, is observed, and ln(rho) ceases to scale with the magnetization. On approaching T_c, both energies become field-dependent, indicating that the polarons are magnetically polarized. Below T_c, the thermopower follows a law S(H) prop. 1/rho (H) as in non saturated ferromagnetic metals.