Magnetoresistance of κ-(BEDT-TTF)2X in normal and mixed states

The interlayer magnetoresistance (MR) of κ-(BEDT-TTF)2X superconductors with X=Cu(NCS)2 and Cu[N(CN)2]Br in fields both above and below Hc2 has been studied. In the former salt, nearly temperature independent oscillations originating from the quantum interference in the magnetic breakdown regime have been directly observed above 2 K in fields 12–14 T. In contrast to the three-dimensional (3D) case, the effect survives at tilting the field from the crystallographic symmetry direction up to the angles as high as 40°. In the other salt clear MB oscillations corresponding to 100% of the Brillouin zone cross-section area have been found above 22 T. Below Hc2, the interlayer resistance is shown to be almost independent of the field direction in a wide angle range around the parallel-to-plane orientation. This result is believed to reflect the strongly two-dimensional nature of the vortex state in the title compounds.