Abstract
We present angle resolved photoemission data on Na-doped We demonstrate that the chemical potential shifts upon doping the system across the insulator to metal transition. The resulting low-energy spectra reveal a gap structure which appears to deviate from the canonical form. To reconcile the measured gap structure with d-wave superconductivity one can understand the data in terms of two gaps, a very small one contributing to the nodal region and a very large one dominating the antinodal region. The latter is a result of the electronic structure observed in the undoped antiferromagnetic insulator. Furthermore, the low-energy electronic structure of the metallic sample contains a two component structure in the nodal direction, and a change in velocity of the dispersion in the nodal direction at roughly 50 meV. We discuss these results in connection with photoemission data on other cuprate systems.
- Received 13 May 2002
DOI:https://doi.org/10.1103/PhysRevB.67.165101
©2003 American Physical Society