Coherent versus incoherent interlayer transport in layered metals

Abstract

The magnetic-field, temperature, and angular dependence of the interlayer magnetoresistance of two different quasi-two-dimensional (2D) organic superconductors is reported. For $\ensuremath{\kappa}\ensuremath{-}(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF}{)}_{2}{\mathrm{I}}_{3},$ where BEDT-TTF is bisethylenedithio-tetrathiafulvalene, we find a well-resolved peak in the angle-dependent magnetoresistance at $\ensuremath{\Theta}=90\ifmmode^\circ\else\textdegree\fi{}$ (field parallel to the layers). This clear-cut proof for the coherent nature of the interlayer transport is absent for ${\ensuremath{\beta}}^{\ensuremath{''}}\ensuremath{-}(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF}{)}_{2}{\mathrm{SF}}_{5}{\mathrm{CH}}_{2}{\mathrm{CF}}_{2}{\mathrm{SO}}_{3}.$ This and the nonmetallic behavior of the magnetoresistance suggest an incoherent quasiparticle motion for the latter 2D metal.