Anomalous multi-order Raman scattering in LaMnO_3: a signature of a quantum lattice effect in a Jahn-Teller crystal

TL;DR

This study investigates multi-order Raman scattering in LaMnO_3, revealing anomalous features linked to a low-energy mode caused by quantum tunneling effects related to Jahn-Teller distortions.

Contribution

It provides evidence that multi-order Raman features are connected to a tunneling transition between Jahn-Teller potential minima, highlighting a quantum lattice effect in LaMnO_3.

Findings

Anomalous sidebands are observed near 25 cm-1.

Multi-order scattering is activated by low-energy electronic tunneling.

Oxygen vibrations dominate the sidebands, with electronic-phonon coupling also involved.

Abstract

The multi-order Raman scattering is studied up to a fourth order for a detwinned LaMnO_3 crystal. Based on a comprehensive data analysis of the polarisation-dependent Raman spectra, we show that the anomalous features in the multi-order scattering could be the sidebands on the low-energy mode at about 25 cm-1. We suggest that this low-energy mode stems from the tunneling transition between the potential energy minima arising near the Jahn-Teller Mn3+ ion due to the lattice anharmonicity, and the multi-order scattering is activated by this low-energy electronic motion. The sidebands are dominated by the oxygen contribution to the phonon density-of-states, however, there is an admixture of an additional component, which may arise from coupling between the low-energy electronic motion and the vibrational modes.