Doping dependence of an n-type cuprate superconductor investigated by   ARPES
  We present an angle resolved photoemission (ARPES) doping dependence study of the n-type cuprate superconductor Nd_2-xCe_xCuO_4, from the half-filled Mott-insulator to the T_c=24K superconductor. In Nd2CuO4, we reveal the charge-transfer band (CTB) 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 ~ x) centered at (pi,0). Further doping leads to the creation of a new hole-like Fermi surface (volume ~ 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. 
N.P. Armitage, F. Ronning, D.H. Lu, C. Kim, A. Damascelli, K.M. Shen,   D.L. Feng, H. Eisaki, Z.-X. Shen (Stanford), P.K. Ma...