Structural disorder and its effect on the superconducting transition temperature in the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br

In this paper, we report direct evidence of a structural transition in the organic superconductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br near 80 K and the effect of disorder on the superconducting transition temperature. By cooling the sample from above 80 K, the interlayer magnetoresistance displays a bumplike feature, which increases sharply with increasing cooling rate. The rapidly cooled sample has a much larger resistivity and a lower transition temperature, which decreases linearly with increasing resistivity near the transition temperature. We propose that rapid cooling quenches the sample into a disordered state. Localized moments in the disordered state reduce the superconducting transition temperature.