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

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.