Pressure-induced low resistive and insulating phases in τ-(EDO-R, R-DMEDT-TTF)2(AuI2)1+y

Abstract A sudden drop of resistance below 7 K was observed in the two-dimensional organic τ-conductor, τ-(EDO- R, R -DMEDT-TTF) 2 (AuI 2 ) 1+y . However, this low resistive state was not associated with superconductivity, since the resistance becomes lower by increasing field. The temperature of the resistance anomaly increased by increasing pressure. Further, the low resistive state turns into high resistive one beyond 1.6 GPa. These behaviors have been observed neither in τ-conductors nor in other organic conductors. Although the electronic properties look quite different from other τ-conductors, Fermi surface areas are only 20% different from the isostructural τ-conductors, i.e. τ-(EDO- S,S -DMEDT-TTF) 2 (AuBr 2 ) 1+y or τ-(P- S,S -DMEDT-TTF) 2 (AuBr 2 ) 1+y . Why so much variety of electronic properties are found in each salt in spite of having similar Fermi surface areas, is an attractive problem but unanswered.