Manifestation of unusual size effects in granular thin films prepared by pulsed laser deposition

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Writers: S. Sergeenkov and L. Cichetto Jr. and J.C.C.A. Diaz and W.B. Bastos and E. Longo and F.M. Araújo-Moreira

Keywords: Nickelates; Thin films; Pulsed laser deposition; Resistivity; Crossover

Abstract: We demonstrate manifestation of some rather unusual size effects in granular thin films prepared by a pulsed laser deposition technique. We observed that the temperature dependence of resistivity ρ(T) notably depends on the relation between the grain size R_g and the film thickness d. Namely, more granular LaNiO₃ thin films (with small values of R_g) grown on LaAlO₃ substrate are found to follow a universal ρ(T)∝T^3/2 law for all the measured temperatures. While less granular thin films (with larger values of R_g), exhibit a more complicated behavior accompanied by a clear-cut crossover (around ), from ρ(T)∝T^3/2 (for ) to ρ(T)∝T (for ). The obtained results are attributed to manifestation of the finite temperature size effects (when an average grain size R_g becomes comparable with the thermal de Broglie wavelength Λ  ) leading to the crossover temperature T_cr∝(d/R_g)².