Resistive transition, magnetoresistance, and anisotropy in La2-xSrxCuO4 single-crystal thin films (JP)

The temperature dependence of the resistivity ρ(T) in the vicinity of the superconducting transition temperature Tc has been measured for thin-film single crystals of La2-xSrxCuO4 as a function of an applied magnetic field, both parallel and perpendicular to the c axis. The resistive transition exhibits characteristic behavior, depending on the Sr concentration x, when a field is applied. For small x the application of a field causes a significant broadening of the resistive transition---a behavior thought to be typical of high-Tc cuprate superconductors---while for x exceeding 0.15, it simply causes a parallel shift of the curves to lower temperatures. From the analysis of the magnetoresistance above Tc based on the theory of field-dependent fluctuation conductivity for layered materials, it is shown that the behavior of the field-induced resistive transition can be ascribed to the flux motion, especially when H perpendicular c. The analysis also shows that the out-of-plane Ginzburg-Landau coherence length ξc(0) increases systematically with x from 0.55 A at x=0.08 to 3 A at x=0.3, while the in-plane Ginsburg-Landau coherence length ξab(0) is almost constant and ξab(0)=31--33 A, irrespective of the value of x as long as Tc remains high. The anisotropy ξab(0)/ξc(0) estimated from these results exceeds 50 at low Sr concentrations and is still larger than 15 even for x>0.1