| dc.description |
The temperature dependences of the in-plane resistivity <sub>ab</sub>(T ) and out-of-plane resistivity <sub>c</sub>(T ) in Bi-2212 crystals covering the region from the underdoped to the overdoped regime have been measured. In the underdoped regime, <sub>ab</sub>(T ) deviates from a linear temperature dependence below a characteristic temperature T <sup>*</sup>, well above T<sub>c</sub>, whose value decreases with increasing hole concentration. For underdoped crystals, <sub>ab</sub>(T) shows a typical S-shaped temperature dependence and <sub>ab</sub> = <sub>0</sub><sup>*</sup>+exp(-/T ) is satisfactorily obeyed over a much wider temperature range from slightly above T<sub>c</sub> up to T <sup>*</sup>. Near the optimal region, the T -linear dependence of <sub>ab</sub>(T ) is maintained over a wide temperature interval. In contrast, a power law <sub>ab</sub>~T<sup>n</sup> (n = 1.5-1.8) is followed in the overdoped regime. As regards the out-of-plane resistivity, on the other hand, <sub>c</sub>(T ) for the underdoped Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>y</sub> crystals shows a semiconductive behaviour, which is well described by the formula <sub>c</sub> = (C<sub>1</sub>/T)exp(C<sub>2</sub>/T ) + C<sub>3</sub>T + C<sub>4</sub>. The difference between the temperature dependences of <sub>c</sub>(T ) in the overdoped Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>y</sub> and Bi<sub>1.85</sub>Pb<sub>0.15</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>8 +</sub> crystals, with basically the same values of T<sub>c</sub> and nearly the same power-law temperature dependences of <sub>ab</sub>(T ) (<sub>ab</sub>~T <sup>1.4</sup>), reveals that the inter-plane disorder in the form of oxygen vacancies and substituted cations acting as an extra blocking layer plays an important role in out-of-plane transport. |
