From very high accuracy reflectivity spectra, we have derived the optical conductivity and estimated the spectral weight up to various cut-off frequencies in underdoped Bi2Sr2CaCu2O8+δ (Bi-2212). We show that, when evaluating the optical spectral weight over the full conduction band (1 eV), the kinetic energy decreases in the superconducting state, unlike in conventional BCS superconductors. As a consequence, the Ferrell-Glover-Tinkham sum rule is not satisfied up to this energy scale. This stands as a very unconventional behavior, contrasted with the overdoped Bi-2212 sample.
@article{arxiv.cond-mat/0404290,
title = {Sum rules and energy scales in BiSrCaCuO},
author = {A. F. Santander-Syro and R. P. S. M. Lobo and N. Bontemps},
journal= {arXiv preprint arXiv:cond-mat/0404290},
year = {2007}
}
Comments
6 pages with 3 figures included. Submitted to NATO Advanced Research Workshop Proceedings (Miami January 2004)