Manifestation of charge/orbital order and charge transfer in temperature-dependent optical conductivity of single-layered Pr0.5Ca1.5MnO4.

Abstract

Half-doped single-layered manganite, [Formula: see text] has shown a charge/orbital order of the e g electrons and CE-type spin order of the t 2g electrons of the Mn ions. A previous experimental study on that system, supported by a simple modelling, has suggested that the charge/orbital ordering play an important role in governing the temperature dependence of optical conductivity of a broad peak around 0.7-0.8\u2009eV. In addition, another peak around 3.5\u2009eV, which is less sensitive to temperature, has been attributed to the charge transfer from O-p\u200a to Mn-e g orbitals. Nevertheless, the theoretical explanation was incomplete as the role of O-p\u200a orbitals was not considered in the model. In this paper, we propose to improve the model by incorporating both Mn-e g and O-p\u200a orbitals. We assume the existence of charge/orbital ordering and investigate how this ordering as well as the charge-transfer phenomenon control the temperature dependence of the optical conductivity. Our results reveal the charge/orbital-ordering peak in the region 0.7-1.2\u2009eV, which is blue-shifted with decreasing temperature, and the charge-transfer peak around 3.5\u2009eV, which is less sensitive to temperature. The capability of our model to capture the general profile and temperature dependence of the optical conductivity suggests the validity of our theory.