Temperature Dependence of In-Plane Resistivity of Ybco

Abstract

Variation of the magnitude and the temperature dependence of the normal state resistivity ρ(T) has been very frequently observed in different Y Ba₂Cu₃O_7−δ (YBCO) single crystals (or YBCO thin films) of the same T_c. We investigated the origin of these changes by analyzing optimally doped and underdoped YBCO thin films (with 7−δ = 6.80−6.95) whose resistivity ρ(T) was characterized by a “superlinear” temperature dependence [with a flattening of ρ(T) below 230K]. We induced oxygen redistribution in these films without any change in the total oxygen content, by either careful annealing over a temperature range of 120–140°C in argon, or by aging at room temperature in air. This procedure leads to a transition from a superlinear ρ(T) towards the linear one, and an increase of both the magnitude of resistivity and T_c. Long-term aging yields a perfectly linear ρ(T). We proposed a filamentary model of the changes in ρ(T), which is based on a thermally activated redistribution of the interchain bridging oxygen O(5) in the chain-layer of YBCO. The results show that a perfectly linear ρ(T) can be observed in YBCO of oxygen content 7−δ as low as 6.8, which is essential for the development of theories of the normal state resistivity and the pseudo-gap state.