| This thesis presents a high-resolution angle-resolved photoemission spectroscopic (ARPES) study of the n-type cuprate superconductor Nd 2−xCexCuO4. The evolution of spectral features is tracked through the full doping range, from the half-filled Mott-insulator to the optimally doped superconductor, concentrating on measurements from the highest-Tc samples.; For the x = 0.15 samples, a comparison of leading edge midpoints between the superconducting and normal states reveals a small, but finite shift of 1.5–2 meV near the (π,0) position, but no observable shift along the zone diagonal near (π/2,π/2). This is interpreted as evidence for an anisotropic superconducting gap in the electron doped materials, which is consistent with the presence of d-wave superconducting order.; In the normal-state electronic structure, it is found that there are regions along the Fermi surface where the near-EF intensity is suppressed and the spectral features are broad in a manner reminiscent of the high-energy “pseudogap” in the underdoped p -type cuprates. However, instead of occurring near (π,0), as in the p-type materials, this pseudogap falls near the intersection of the underlying Fermi surface with the antiferromagnetic Brillouin zone boundary. The fact that the high-energy pseudogap and the superconducting gap have different momentum space symmetries, points to a nonpairing origin of the pseudogap in the extreme underdoped regime of the p-type materials.; In the undoped compound Nd2CuO4, for the first time the charge transfer band is revealed. As electrons are doped to the system, spectral weight forms near-EF with a concomitant decrease in the intensity of the charge transfer band. The momentum dependence of this near-E F spectral weight is shown and it is demonstrated at least phenomenologically how the large Fermi surface of the x = 0.15 material forms. These findings shed light on the nature of the Mott gap, its doping dependence, as well as the anomalous transport properties of the electron-doped cuprates. |
