Pressure-Induced Insulating State in an Organic Superconductor

The electronic-transport properties of the quasi-two-dimensional organic superconductor $\beta$''-(BEDT-TTF)2SF5CH2CF2SO3, where BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene, have been investigated in magnetic fields up to 15 T and under hydrostatic pressure up to about 14 kbars. Shubnikov\textendash{}de Haas data reveal a nonmonotonic pressure dependence of the holelike Fermi surface, a roughly linear increase of the electron g factor, and an approximately linear decrease of the cyclotron effective mass. By assuming that the latter reflects the pressure-induced reduction of the superconducting coupling parameter $\lambda$ the rapid reduction of the superconducting transition temperature Tc(p) can be reasonably well described by the modified McMillan equation. Above about 12 kbars the material becomes insulating with an activated resistive behavior. This first-order metal-insulator transition has a hysteresis of about 3 kbars. This unexpected behavior is assumed to be of structural origin, although clear changes of electronic band-structure properties precede the phase transition.     «

The electronic-transport properties of the quasi-two-dimensional organic superconductor $\beta$''-(BEDT-TTF)2SF5CH2CF2SO3, where BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene, have been investigated in magnetic fields up to 15 T and under hydrostatic pressure up to about 14 kbars. Shubnikov\textendash{}de Haas data reveal a nonmonotonic pressure dependence of the holelike Fermi surface, a roughly linear increase of the electron g factor, and an approximately linear decrease of the cyc...     »