The magnetic-field, temperature, and angular dependence of the interlayer magnetoresistance of two different quasi-two-dimensional (2D) organic superconductors is reported. For $\kappa -(\mathrm{BEDT}-\mathrm{TTF}{)}_2{\mathrm{I}}_3,$ where BEDT-TTF is bisethylenedithio-tetrathiafulvalene, we find a well-resolved peak in the angle-dependent magnetoresistance at $\Theta =90\mathrm{}°$ (field parallel to the layers). This clear-cut proof for the coherent nature of the interlayer transport is absent for ${\beta }^{″}-(\mathrm{BEDT}-\mathrm{TTF}{)}_2{\mathrm{SF}}_5{\mathrm{CH}}_2{\mathrm{CF}}_2{\mathrm{SO}}_3.$ This and the nonmetallic behavior of the magnetoresistance suggest an incoherent quasiparticle motion for the latter 2D metal.

• Received 8 March 2002

DOI:https://doi.org/10.1103/PhysRevB.65.180506