Anomalous electronic susceptibility inBi2Sr2CuO6+δand comparison with other overdoped cuprates

It is widely believed that the study of the unusual normalstate properties in cuprates is very important to understand the mechanism that underlies high-Tc superconductivity. The underdoped part of the generic critical temperature carrier density phase diagram of high-Tc cuprate superconductors ~HTSC’s ! is characterized by pseudogap effects which have been extensively investigated through various experimental approaches. The overdoped regime, considered as having the ‘‘classical’’ electronic properties of a normal metal, has been much less studied. Recent theoretical and experimental results have shown that there is considerable evidence to the contrary. In a conventional Fermi liquid ~FL!, both the electronic spin susceptibility ( x s) and electronic specific heat coefficient~g! are, in a first approximation, independent ofT. In the cuprates, by contrast, x s and g present both positive slopes in the underdoped regime 1 and negative slopes in the overdoped one. 2‐5 At optimal hole concentration, where Tc takes on its maximum value, x s and g remain temperature independent. Moreover, the first temperature corrections for several physical parameters measured in the overdoped range do not correspond to those of the usual FL. For instance, the electronic spin susceptibility x s shows a close to linear decrease with T in this overdoped range. 6 This trend can be also related to a similar behavior observed in the electronic specific heat and in the Knight shift 7,8 as well as to the anomalous T dependence of the thermopower in this doping range. 9,10