Pseudogap behavior of phase-separated Sm$_{1-x}$Ca$_x$MnO$_3$ : A comparative photoemission study with double exchange

TL;DR

This study investigates the pseudogap phenomena in phase-separated Sm$_{1-x}$Ca$_x$MnO$_3$ using photoemission, comparing it with La$_{1-x}$Sr$_x$MnO$_3$, revealing differences in energy gap behavior related to structural distortions.

Contribution

It provides a comparative analysis of pseudogap behavior in phase-separated and double exchange manganites, emphasizing structural influences on electronic properties.

Findings

Pseudogap grows with phase separation leading to metal-insulator transition

Differences in energy gaps are linked to MnO$_6$ octahedral distortions

Phase separation models explain the observed electronic behavior

Abstract

Using valence band photoemission we have demonstrated the presence of a pseudogap in the near Fermi level electronic spectrum of some of the mixed phase compositions of Sm$_{1-x}$Ca$_x$MnO$_3$ system. The pseudogap was found to grow in size over a large region of the phase diagram of this system, finally leading to a metal-insulator transition. We have made a study comparing the near Fermi level behaviors of this system to those of a canonical double exchange system, namely, La$_{1-x}$Sr$_x$MnO$_3$. This study intends to highlight one of the important differences between the phase separated and double exchange colossal magnetoresistance systems in the nature of their energy gaps across the metal-insulator transitions. These differences could be ascribed to the distortions in the MnO$_6$ octahedra of their structures that regulate the localization of charge carriers. We have discussed our results from the point of view of models based on the idea of phase separation.