Field-Induced Metal-Insulator Transition in a Two-Dimensional Organic Superconductor

The quasi-two-dimensional organic superconductor β^''-(BEDT-TTF)₂SF₅CH₂CF₂SO₃ (Tc≈4.4K) shows very strong Shubnikov--de Haas (SdH) oscillations which are superimposed on a highly anomalous steady background magnetoresistance, Rb. Comparison with de Haas--van Alphen oscillations allows a reliable estimate of Rb which is crucial for the correct extraction of the SdH signal. At low temperatures and high magnetic fields insulating behavior evolves. The magnetoresistance data violate Kohler's rule, i.e., cannot be described within the framework of semiclassical transport theory, but converge onto a universal curve appropriate for dynamical scaling at a metal-insulator transition.