Magnetic field-dependent interplay between incoherent and Fermi liquid transport mechanisms in low-dimensional tau phase organic conductors
Abstract
We present an electrical transport study of the 2-dimensional (2D) organic conductor tau-(P-(S,S)-DMEDT-TTF)2(AuBr)2(AuBr2)y (y = 0.75) at low temperatures and high magnetic fields. The inter-plane resistivity rhozz increases with decreasing temperature, with the exception of a slight anomaly at 12 K. Under a magnetic field B, both rhozz and the in-plane resistivity plane rhoxx show a pronounced negative and hysteretic magnetoresistance with Shubnikov de Haas (SdH)oscillations being observed in some (high quality)samples above 15 T. Contrary to the predicted single, star-shaped, closed orbit Fermi surface from band structure calculations (with an expected approximate area of 12.5% of AFBZ), two fundamental frequencies Fl and Fh are detected in the SdH signal. These orbits correspond to 2.4% and 6.8% of the area of the first Brillouin zone(AFBZ), with effective masses Fl = 4.0 +/- 0.5 and Fh = 7.3 +/- 0.1. The angular dependence, in tilted magnetic fields of Fl and Fh, reveals the 2D character of the FS and Angular dependent magnetoresistance (AMRO) further suggests a FS which is strictly 2-D where the inter-plane hopping tc is virtually absent or incoherent. The Hall constant Rxy is field independent, and the Hall mobility increases by a factor of 3 under moderate magnetic fields. Our observations suggest a unique physical situation where a stable 2D Fermi liquid state in the molecular layers are incoherently coupled along the least conducting direction. The magnetic field not only reduces the inelastic scattering between the 2D metallic layers, but it also reveals the incoherent nature of interplane transport in the AMRO spectrum. The apparent ferromagnetism of the hysteretic magnetoresistance remains an unsolved problem.
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