Doping-induced change in the interlayer transport mechanism of Bi2Sr2CaCu2O8+δ near the superconducting transition temperature

We perform a detailed study of temperature, bias, and doping dependence of interlayer transport in the layered high temperature superconductor Bi(2)Sr(2)CaCu(2)O(8+delta). We observe that the shape of interlayer characteristics in underdoped crystals exhibits a remarkable crossover at the superconducting transition temperature: from thermal activation-type above T(c) to almost T-independent quantum tunneling-type below T(c). Our data provide insight into the nature of interlayer transport and indicate that its mechanism changes with doping: from the conventional single quasiparticle tunneling in overdoped to a progressively increasing Cooper pair contribution in underdoped crystals.