Is the resistance upturn around 50K related to the Fermi surface area in τ-(EDO-R, R-DMEDT-TTF)2(AuBr2)1+y?

Abstract From our previous observation, it is known that τ-(EDO- R,R -DMEDT-TTF) 2 (AuBr 2 ) 1+ y ( y ≤ 0.875) exhibits strong sample dependence in the temperature dependence of its resistance R ( T ). Some samples are metallic down to 4.2 K, while others show upturn below around 50 K. To investigate the origin of the sample dependence, we performed Shubnikov-de Haas (SdH) effect for four samples. Here two samples show metallic behavior, while other samples exhibit nonmetallic below 50 K. From the observation of the SdH oscillation, we detect two series of two-dimensional (2D) Fermi surfaces (FS's) pockets for all samples. Interestingly, we find slight scatter in the area of FS, but no correlation is found between R ( T ) and FS area. The origin of the slight difference in the FS areas is discussed in terms of possible difference in the band filling.