Doping Dependence of ann-Type Cuprate Superconductor Investigated by Angle-Resolved Photoemission Spectroscopy

We present an angle-resolved photoemission doping dependence study of the $n$-type cuprate superconductor ${\mathrm{Nd}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_{4\pm \delta }$, from the half-filled Mott insulator to the $T_c=24\mathrm{}\mathrm{K}$ 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 $\sim x$) centered at $(\pi ,0\mathrm{})$. Further doping leads to the creation of a new holelike Fermi surface (volume $\sim 1+x$) centered at $(\pi ,\pi )$. These findings shed light on the Mott gap, its doping evolution, as well as the anomalous transport properties of the $n$-type cuprates.