Pseudogap, Superconducting Gap, and Fermi Arc in High-Tc Cuprates Revealed by Angle-Resolved Photoemission Spectroscopy

We present an overview of angle-resolved photoemission spectroscopy (ARPES) studies of high-temperature cuprate superconductors aiming at elucidating the relationship between the superconductivity, the pseudogap, and the Fermi arc. ARPES studies of underdoped samples show a momentum dependence of the energy gap below T-c which deviates from a simple d-wave form, suggesting the coexistence of multiple energy scales in the superconducting state. Hence, two distinct energy scales have been introduced, namely, the gap near the node (characterized by Delta(0)) and in the antinodal region (characterized by Delta*). Dichotomy between them has been demonstrated from the material, doping, and temperature dependence of the energy gap. While Delta* at the same doping level is approximately material independent, Delta(0) shows a strong material dependence tracking the magnitude of T-c,T-max. The anti-nodal gap does not close at T-c in contrast to the gap near the node which follows something closer to a BCS-like temperature dependence. An effective superconducting gap Delta(sc) defined at the end point of the Fermi arc is found to be proportional to T-c's in various materials.