Resistivity anomaly in the vicinity of a structural phase transition in La_1−xSr_xMnO₃

Abstract

The resistivity ρ has been measured up to 900 K in La_1−xSr_xMnO₃ ( 0 <∼ x <∼ 0 . 1 5 ) single crystals to investigate the nature of charge transport phenomena both above and below the cooperative Jahn-Teller orbital-ordering temperature ( T_JT) . At high temperatures above T_JT , ρ is almost temperature independent for LaMnO 3 whereas ρ exhibits a strong temperature dependence for x > 0 samples. In the orbitally ordered state, ρ can be described well by a small-polaron hopping model with ρ ( T ) = ρ 0 exp ( E_ρ / k T ) . We observe that both above and below T_JT the resistivity can be fitted with the same activation energy E ρ but with different prefactor ρ 0 for x > 0 samples. Though ρ decreases monotonically with increasing doping concentration, E_ρ is almost independent of Sr concentration up to x = 0.10 and then decreases rapidly above this value of x.