Transition between two ferromagnetic states driven by orbital ordering in La_{0.88}Sr_{0.12}MnO_3

TL;DR

This study reveals how orbital ordering drives a transition from ferromagnetic metal to ferromagnetic insulator in La_{0.88}Sr_{0.12}MnO_3, highlighting the orbital degree of freedom's crucial role in the metal-insulator transition.

Contribution

It provides direct experimental evidence and theoretical understanding of the orbital degree's influence on the phase transition in lightly doped manganites.

Findings

Orbital ordering occurs below T_{OO}=145 K despite reduced Jahn-Teller distortion.

The transition involves a change from metallic to insulating ferromagnetic state.

Theoretical models confirm the importance of orbital degrees under strong electron correlation.

Abstract

A lightly doped perovskite mangantite La_{0.88}Sr_{0.12}MnO_3 exhibits a phase transition at T_{OO}=145 K from a ferromagnetic metal (T_C=172 K) to a novel ferromagnetic insulator.We identify that the key parameter in the transition is the orbital degree of freedom in e_g electrons. By utilizing the resonant x-ray scattering technique, orbital ordering is directly detected below T_{OO}, in spite of a significant diminution of the cooperative Jahn-Teller distortion. The new experimental features are well described by a theory treating the orbital degree of freedom under strong electron correlation. The present experimental and theoretical studies uncover a crucial role of the orbital degree in the metal-insulator transition in lightly doped manganites.