Chemical potential shift and spectral weight transfer in Pr$_{1-x}$Ca$_x$MnO$_3$ revealed by photoemission spectroscopy

Abstract

We have studied the chemical potential shift and changes in the electronic density of states near the Fermi level ($E_F$) as a function of carrier concentration in Pr$_{1-x}$Ca$_x$MnO$_3$ (PCMO, $0.2 \le x \le 0.65$) through the measurements of photoemission spectra. The results showed that the chemical potential shift was suppressed for $x \agt 0.3$, where the charge exchange (CE)-type antiferromagnetic charge-ordered state appears at low temperatures. We consider this observation to be related to charge self-organization such as stripe formation on a microscopic scale in this composition range. Together with the previous observation of monotonous chemical potential shift in La$_{1-x}$Sr$_x$MnO$_3$, we conclude that the tendency toward the charge self-organization increases with decreasing bandwidth. In the valence band, spectral weight of the Mn 3$d$ $e_g$ electrons in PCMO was transferred from $\sim$ 1 eV below $E_F$ to the region near $E_F$ with hole doping, leading to a finite intensity at $E_F$ even in the paramagnetic insulating phase for $x \agt 0.3$, probably related with the tendency toward charge self-organization. The finite intensity at $E_F$ in spite of the insulating transport behavior is consistent with fluctuations involving ferromagnetic metallic states.