Magnetoresistance peak in the mixed state of the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br

In this letter, the authors report transport measurements with field and current parallel to the b axis (perpendicular to the conducting plane) in the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br. The isothermal magnetoresistance R(H) displays a peak effect as a function of field. The peak resistance is substantially larger than that in large fields. The results are in sharp contrast to the conventional dissipation mechanisms in the mixed state of anisotropic superconductors, as in the case of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. Comparison with H{sub c2}(T) obtained from magnetic measurements shows that the peak effect in R(H) occurs in the mixed state. Analysis of the data suggests a much larger Josephson junction resistance in the mixed state than that in the normal state, indicative of a new charge transport scattering mechanism in the presence of vortices