Effect of disorder on the charge-carrier dynamics in κ-(D8-ET)2Cu[N(CN)2]Br

We have applied resistance fluctuation spectroscopy to study the intrinsic low-frequency dynamics of the charge carriers in the system kappa-(D-8-ET)(2)Cu[N(CN)(2)]Br for two different cooling rates. A strong increase of both the resistance and the noise level is observed below the thermodynamic glass-transition temperature T-g. Surprisingly, the data of the normalized spectral weight <(delta R)(2)>/R-2 fall on top of each other for both cooling rates except for temperatures near the Mott critical point (T-0 similar or equal to 35 K) and below 28K. The suppression of the peak in <(delta R)(2)>/R-2 associated with the Mott transition suggests that disorder is an additional parameter in the generalized phase diagram. The enhanced noise level below 28K might be explained by a disorder-induced staggered magnetic moment in the metallic state close to the antiferromagnetic Mott insulator. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim