Coherent versus incoherent interlayer transport in layered metals

The magnetic-field, temperature, and angular dependence of the interlayer magnetoresistance of two different quasi-two-dimensional (2D) organic superconductors is reported. For κ-(BEDT-TTF) 2 I 3 , where BEDT-TTF is bisethylenedithio-tetrathiafulvalene, we find a well-resolved peak in the angle-dependent magnetoresistance at Θ=90° (field parallel to the layers). This clear-cut proof for the coherent nature of the interlayer transport is absent for β"-(BEDT-TTF) 2 SF 5 CH 2 CF 2 SO 3 . This and the nonmetallic behavior of the magnetoresistance suggest an incoherent quasiparticle motion for the latter 2D metal.