Ultrafast Polaron Dynamics in Layered and Perovskite Manganites: 2D and 3D Polarons

TL;DR

This study investigates ultrafast polaron dynamics in layered and perovskite manganites, revealing how temperature and dimensionality influence electron relaxation processes and their connection to spin and phonon interactions.

Contribution

It provides new insights into the sub-picosecond polaron redressing mechanisms and their dependence on material dimensionality and temperature in manganites.

Findings

Polaron redressing occurs in hundreds of femtoseconds above Tc.

Dimensionality affects the relaxation times and mechanisms.

A crossover to electron-phonon relaxation is observed below Tc.

Abstract

We have studied the sub-picosecond quasiparticle dynamics in the perovskite manganite La0.7Ca0.3MnO3 and the layered manganite La1.4Sr1.6Mn2O7 using ultrafast optical spectroscopy. We found that for T > TC, initial relaxation proceeds on the time scale of several hundred femtoseconds and corresponds to the redressing of a photoexcited electron to its polaronic ground state. The temperature and dimensionality dependence of this polaron redressing time provides insight into the relationship between polaronic motion and spin dynamics on a sub-picosecond time scale. We also observe a crossover to a more conventional electron-phonon relaxation in the ferromagnetic metallic phase below Tc.