Global trends in the interplane penetration depth of layered superconductors

Abstract

We report on generic trends in the behavior of the interlayer penetration depth ${\ensuremath{\lambda}}_{c}$ of several different classes of quasi-two-dimensional superconductors including high-${T}_{c}$ cuprates, ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4},$ transition-metal dichalcogenides and organic materials of the $(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF}{)}_{2}X$ series. An analysis of these trends reveals two distinct patterns in the scaling between the values of ${\ensuremath{\lambda}}_{c}$ and the magnitude of the c-axis dc conductivity ${\ensuremath{\sigma}}_{\mathrm{dc}}:$ 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 $\ensuremath{\simeq}{10}^{2})$ of the energy scale ${\ensuremath{\Omega}}_{C}$ 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.