Comment to the paper "In-plane spectral weight shift of charge-carriers in YBa2Cu3O(6.9)" by A. V. Boris et al., Science 304, p. 708 (2004)

Recently, A. V. Boris and colleagues claimed to deduce a decrease of intraband spectral weight (SW), and a transfer of SW from intraband to inter-band frequencies, when optimally-doped or slightly underdoped cuprates become superconducting [A. V. Boris et al., Science 304, p. 708 (2004)]. We show that, while their data agree with others [H. J. A. Molegraaf et al., Science 295, p. 2239 (2002) ; A.F. Santander-Syro et al., Europhys.Lett 62, p. 568 (2003)], their analysis is flawed. They cannot disprove the results which yield a superconductivity-induced increase of intraband SW, and a transfer of SW from high to low frequencies, in underdoped or nearly optimally doped Bi-2212.