Temperature dependence of the resistivity of oxygen controlled Bi2Sr2CaCu2O8+delta thin films: pseudogap effect

We have investigated the temperature dependence of the resistivity rho(ab)( T) of epitaxial c-axis oriented Bi2Sr2CaCu2O8+delta thin films, at differen t oxygen content. A film is brought, by successive annealing treatments, fr om maximally overdoped (T-c = 62 K) to strongly underdoped (T-c < 4.2 K) st ill metallic states (d rho/dT > 0). When decreasing T, rho(ab)(T) for overd oped states departs from linearity with an upward curvature whereas for opt imally doped and underdoped states it drops from linearity with a downturn starting at a temperature T*, which increases with decreasing T-c, i.e. dec reasing carrier concentration. This characteristic temperature T* is in clo se agreement with the values reported in the literature from ARPES measurem ents on Bi2Sr2CaCu2O8+delta single crystals, attributed to the opening of a pseudogap in the excitation spectrum. It is proposed that the faster decre ase of rho(ab)(T) observed below T* has the same origin. (C) 1999 Elsevier Science B.V. All rights reserved.