Global trends in the interplane penetration depth of layered superconductors

We report on generic trends in the behavior of the interlayer penetration depth lambda(c) of several different classes of quasi-two-dimensional superconductors including high-T-c cuprates, Sr2RuO4, transition-metal dichalcogenides and organic materials of the (BEDT-TTF)(2)X series. An analysis of these trends reveals two distinct patterns in the scaling between the values of lambda(c) and the magnitude of the c-axis dc conductivity sigma(dc): one realized in the systems with a ground state formed from well-defined quasiparticles, and the other seen in systems in which the quasiparticles are not well defined. The latter pattern is found primarily in underdoped cuprates, and indicates a dramatic enhancement (a factor similar or equal to10(2)) of the energy scale Omega(C) associated with the formation of the condensate compared to the data for conventional materials. We discuss the implication of these results on the understanding of superconductivity in high-T-c cuprates.