Phonon-Metamorphosis in Ferromagnetic Manganite Films: Probing the Evolution of an Inhomogeneous State

TL;DR

This paper investigates phonon anomalies in La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ films, revealing phonon metamorphosis linked to inhomogeneous Jahn-Teller distortions and a Griffiths-like phase near the ferromagnetic transition.

Contribution

It provides the first observation of all eight phonon modes in the metallic phase of LSMO and connects phonon behavior to inhomogeneous lattice distortions and magnetic phases.

Findings

Phonon modes merge near the ferromagnetic transition temperature.

Two new phonon modes develop with strong resonances above $T_C$.

Susceptibility measurements indicate a Griffiths-like phase.

Abstract

The analysis of phonon anomalies provides valuable information about the cooperative dynamics of lattice, spin and charge degrees of freedom. Significant is the anomalous temperature dependence of the external modes observed in La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ (LSMO) films. The two external modes merge close to the ferromagnetic to paramagnetic transition at $T_C$ and, moreover, two new modes evolve in this temperature range with strong resonances at slightly higher frequencies. We propose that this observed phonon metamorphosis probes the inhomogeneous Jahn-Teller distortion, manifest on the temperature scale $T_C$. The analysis is based on the first observation of all eight phonon modes in the metallic phase of LSMO and on susceptibility measurements which identify a Griffiths-like phase.