Temperature-dependent photoemission spectral weight transfer and chemical potential shift in Pr$_{1-x}$Ca$_x$MnO$_3$ : Implications for charge density modulation

TL;DR

This study investigates how temperature affects the electronic structure and chemical potential in Pr$_{1-x}$Ca$_x$MnO$_3$, revealing phase-dependent spectral changes and implications for charge density modulation.

Contribution

It provides the first detailed analysis of temperature-dependent spectral weight transfer and chemical potential shifts in PCMO across different doping levels and phases.

Findings

Spectral weight near $E_F$ increases with temperature in charge-ordered phases.

Chemical potential shifts with temperature due to gap opening in FI and CO phases.

Spectral weight transfer with hole doping is suppressed at low temperatures.

Abstract

We have studied the temperature dependence of the photoemission spectra of Pr$_{1-x}$Ca$_x$MnO$_3$ (PCMO) with $x=0.25$, 0.3 and 0.5. For $x=0.3$ and 0.5, we observed a gap in the low-temperature CE-type charge-ordered (CO) phase and a pseudogap with a finite intensity at the Fermi level ($E_F$) in the high-temperature paramagnetic insulating (PI) phase. Within the CO phase, the spectral intensity near $E_F$ gradually increased with temperature. These observations are consistent with the results of Monte Carlo simulations on a model including charge ordering and ferromagnetic fluctuations [H. Aliaga {\it et al.} Phys. Rev. B {\bf 68}, 104405 (2003)]. For $x=0.25$, on the other hand, little temperature dependence was observed within the low-temperature ferromagnetic insulating (FI) phase and the intensity at $E_F$ remained low in the high-temperature PI phase. We attribute the difference in the temperature dependence near $E_F$ between the CO and FI phases to the different correlation lengths of orbital order between both phases. Furthermore, we observed a chemical potential shift with temperature due to the opening of the gap in the FI and CO phases. The doping dependent chemical potential shift was recovered at low temperatures, corresponding to the disappearance of the doping dependent change of the modulation wave vector. Spectral weight transfer with hole concentration was clearly observed at high temperatures but was suppressed at low temperatures. We attribute this observation to the fixed periodicity with hole doping in PCMO at low temperatures.