Magnetic-field-dependent interplay between incoherent and Fermi liquid transport mechanisms in low-dimensional τ-phase organic conductors (original) (raw)

We present an electrical transport study of the 2-dimensional (2D) organic conductor τ -(P-(S,S)-DMEDT-TTF) 2 (AuBr) 2 (AuBr 2 ) y (where y ∼ 0.75) at low temperatures and high magnetic fields. The inter-plane resistivity ρ zz increases with decreasing temperature, with the exception of a slight anomaly at 12 K. Under a magnetic field B, both ρ zz and the in-plane resistivity plane ρ xx show a pronounced negative and hysteretic magnetoresistance. In spite of a negative residual resistivity ratio in zero field, Shubnikov de Haas (SdH) oscillations are observed in some (high quality) samples above 15 T. Furthermore, contrary to the single closed orbit Fermi surface predicted from band structure calculations (where a single star-shaped FS sheet with an area of ∼ 12.5% of A F BZ is expected), two fundamental frequencies F l and F h are detected in the SdH signal. These orbits correspond to 2.4% and 6.8% of the area of the first Brillouin zone (A BZ ), with effective masses µ l = 4.0 ± 0.5 and µ h = 7.3 ± 0.1 respectively. The angular dependence, in tilted magnetic fields, of F l and F h , reveals a 2D character of the FS, but no evidence for warping along the k z direction ( e.g., the absence of a beating effect in the SdH signal) is observed. Angular dependent magnetoresistance (AMRO) fur-