Doping dependence of an n-type cuprate superconductor investigated by angle-resolved photoemission spectroscopy.

We present an angle-resolved photoemission doping dependence study of the $n$-type cuprate superconductor ${\mathrm{Nd}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}}$, from the half-filled Mott insulator to the ${T}_{c}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}24\mathrm{K}$ superconductor. In ${\mathrm{Nd}}_{2}{\mathrm{CuO}}_{4}$, we reveal the charge-transfer band for the first time. As electrons are doped into the system, this feature's intensity decreases with the concomitant formation of near- ${E}_{F}$ spectral weight. At low doping, the Fermi surface is an electron-pocket (with volume $\ensuremath{\sim}x$) centered at $(\ensuremath{\pi},0)$. Further doping leads to the creation of a new holelike Fermi surface (volume $\ensuremath{\sim}1+x$) centered at $(\ensuremath{\pi},\ensuremath{\pi})$. These findings shed light on the Mott gap, its doping evolution, as well as the anomalous transport properties of the $n$-type cuprates.