Chemical potential shift and spectral-weight transfer inPr1−xCaxMnO3revealed 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 ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ (PCMO, $0.2\ensuremath{\leqslant}x\ensuremath{\leqslant}0.65$) through the measurements of photoemission spectra. The results showed that the chemical potential shift was suppressed for $x\ensuremath{\gtrsim}0.3$, 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 ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$, we conclude that the tendency toward the charge self-organization increases with decreasing bandwidth. In the valence band, spectral weight of the Mn $3d$ ${e}_{g}$ electrons in PCMO was transferred from $\ensuremath{\sim}1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ 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 $x\ensuremath{\gtrsim}0.3$, 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.