Evolution of a metal to insulator transition in Ca2-xNaxCuO2Cl2 as seen by angle-resolved photoemission -: art. no. 165101

We present angle resolved photoemission data on Na-doped Ca2CuO2Cl2. 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 d(x)(2)-y(2proportional to)\ cos(k(x)a)-cos(k(y)a)\ 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.