Magnetoresistance and Hall effect in tetramethyl-tetraselenafulvalene-phosphorus hexafloride [(TMTSF)2PF6]

We have measured the magnetoresistance and Hall effect of tetramethyl-tetraselena-fulvalene-phosphorus hexafloride as a function of temperature, magnetic field for several orientations, and electric field. For temperatures well below the metal-insulator transition we find a large positive Hall coefficient and positive magnetoresistance, indicating carrier mobilities greater than ${10}^5$ ${\mathrm{cm}}^2$/V sec at 4.2 K. The magnetoresistance is highly anisotropic for field orientations in theplane perpendicular to the highly conducting axis, indicating a quasi-two-dimensional band structure. The nonlinear conductivity seen with small electric fields below the metal-insulator transition has approximately the same magnetic-field behavior as does the Ohmic conductivity at the same temperature.