Rearrangement of the orbital-ordered state at the metal-insulator transition ofLa7/8Sr1/8

Orbiton-mediated multiphonon scattering inLa1−xSrxMnO3

“…In contrast, the FMI sample (x = 0.125) exhibits a rather strong suppression of the second-order signal through the metal-insulator transition at T C ≈ 185 K where the rearrangement of orbital ordering takes place. 10 This suggests a relationship between the observed multi-phonon scattering and the change of an orbital ordering form through the CAF/FMI phase boundary (see below).…”

“…In the FMI phase a new type of orbital state evolves from the LaMnO 3 -type orbital state upon cooling below T C ≈ 185 K while suppressing the JT distortions. 10 Although its exact form is not known, there exists evidence that orbital polarons are an essential part of a new orbital ordered state. 10,13 Most probably, thus, the orbital ordering of the FMI phase will be given as a combination of an orbital polaron and a d 3x 2 −r 2 /d 3y 2 −r 2 orbital.…”

“…10 Although its exact form is not known, there exists evidence that orbital polarons are an essential part of a new orbital ordered state. 10,13 Most probably, thus, the orbital ordering of the FMI phase will be given as a combination of an orbital polaron and a d 3x 2 −r 2 /d 3y 2 −r 2 orbital. Noticeably, the binding energy of orbital polarons, ∆ op = 0.6 eV, is much smaller than the JT gap of 2 eV.…”

“…In par-ticular, this is related to a fluctuation of the underlying orbitals in the FMI phase. 10,13 The weakening of orbitonphonon coupling can account for a giant softening of the two-phonon frequency. Therefore, we come to the conclusion that the multiphonon scattering in LaMnO 3 relies strongly on the orbital ordered pattern.…”

“…Furthermore, their doping dependence can give further clues because the orbital ordering undergoes a transition while crossing the phase boundary between the canted antiferromagnetic insulating (CAF) and ferromagnetic insulating (FMI) state. 10 In this paper we report on Raman scattering measurements of single crystalline La 1−x Sr x MnO 3 (x=0, 0.06, 0.09 and 0.125), focusing on the higher energy regime. For x = 0 we observe multi-phonon scattering up to fourth order of the one-phonon modes at frequencies between 490 and 640 cm −1 .…”