Two Component Heat Diffusion Observed in CMR Manganites

TL;DR

This study investigates the ultrafast electron, lattice, and spin dynamics in CMR manganites LaMnO3 and La0.7Ca0.3MnO3 using pump-probe spectroscopy, revealing a two-component heat diffusion process and developing a modified energy transfer model.

Contribution

The paper introduces a modified three temperature model that accounts for film-to-substrate heat diffusion in CMR manganites, providing a comprehensive understanding of their ultrafast dynamics.

Findings

Identification of an additional long-term heat diffusion component.

Development of a consistent three temperature model including substrate effects.

Full explanation of sub-picosecond non-thermal dynamics in both insulating and metallic manganites.

Abstract

We investigate the low-temperature electron, lattice, and spin dynamics of LaMnO_3 (LMO) and La_0.7Ca_0.3MnO_3 (LCMO) by resonant pump-probe reflectance spectroscopy. Probing the high-spin d-d transition as a function of time delay and probe energy, we compare the responses of the Mott insulator and the double-exchange metal to the photoexcitation. Attempts have previously been made to describe the sub-picosecond dynamics of CMR manganites in terms of a phenomenological three temperature model describing the energy transfer between the electron, lattice and spin subsystems followed by a comparatively slow exponential decay back to the ground state. However, conflicting results have been reported. Here we first show clear evidence of an additional component in the long term relaxation due to film-to-substrate heat diffusion and then develop a modified three temperature model that gives a consistent account for this feature. We confirm our interpretation by using it to deduce the bandgap in LMO. In addition we also model the non-thermal sub-picosecond dynamics, giving a full account of all observed transient features both in the insulating LMO and the metallic LCMO.