Unconventional magnetic field and pressure dependences of the ground state of the low-dimensional organic superconductor (BEDO-TTF)(2)ReO4 center dot H2O

Magnetotransport experiments have been carried out in the two-dimensional organic metal (BEDO-TTF)(2)ReO4 . H2O at temperatures down to 0.4 K and under hydrostatic pressure up to 11 kbar. When measured in magnetic field of a few teslas, the magnetoresistance is large and a steep resistance rise is observed below 4 K, which, as is the case for quasi-one-dimensional TMTSF-based compounds, is the signature of a spin density wave condensation. As already observed at ambient pressure, two series of Shubnikov-de Haas oscillations, linked to hole and electron orbits, are evidenced in the applied pressure range from 3.5 to 11 kbar. Both hole and electron orbit; oscillation frequencies (respectively noted F-h and F-e) increase strongly as the pressure increases (dln(F-h,F-e)/dP = 0.07 kbar(-1)), while their ratio remains unchanged (F-h/F-e = 2). As the applied pressure increases, both cyclotron masses either slowly decrease or remain constant, keeping low values when compared to other 2D compounds.