Antinodal quasiparticles below and above T_Curie in the CMR oxide La_(2-2x)Sr_(1+2x)Mn_(2)O_(7) with x=0.36

TL;DR

This study uses ARPES to investigate quasiparticle behavior in the CMR oxide La_{2-2x}Sr_{1+2x}Mn_{2}O_{7} at different doping levels, revealing persistent quasiparticles above T_Curie and insights into their renormalization.

Contribution

It provides new ARPES data showing quasiparticles above T_Curie in a bilayered CMR manganite, challenging previous conflicting results and suggesting weak spin coupling effects.

Findings

Quasiparticles are observed at and around (pi, 0) in k-space for x=0.36.

Quasiparticle features persist up to 50 K above T_Curie.

Electronic states show renormalization due to bosonic coupling.

Abstract

In light of recent conflicting angle resolved photoemission studies on the bilayered colossal magnetoresistant (CMR) manganite La_{2-2x}Sr_{1+2x}Mn_{2}O_{7} (0.36< x< 0.40), new ARPES data are presented for x=0.36 and 0.40, showing only for the former clear quasiparticle-like features at and around the (pi, 0)-point in k-space. The electronic states are clearly renormalised, both as regards their dispersion relation and lifetime due to coupling to bosonic degrees of freedom. Importantly, both the existence of quasiparticles and their renormalisation survive well into the paramagnetic state, up to 50 K above T_Curie. This argues against strong coupling to spin modes and raises questions regarding the nature of the paramagnetic insulating phase.