This paper has been withdrawn by the authors because the results were incorrect due to the use of an impurity solver that fails at large interaction strength and above half-filling. This led, first, to the development of a new impurity solver (arXiv:1202.5814 or Phys.Rev. B 86, 085133 (2012)) and, second, to a complete revision of the thermopower results with different conclusions. Therefore a new paper on thermopower was submitted (arXiv:1209.4349) and the present one withdrawn.
@article{arxiv.1104.4537,
title = {Optimal doping and entropic origin of giant thermopower in doped Mott insulators},
author = {Louis-Francois Arsenault and B. Sriram Shastry and Patrick Semon and A. -M. S. Tremblay},
journal= {arXiv preprint arXiv:1104.4537},
year = {2012}
}