c-axis magnetoconductivity of anisotropic superconducting single crystals:The density-of-states fluctuation scenario

The c-axis magnetoconductivity (B parallel to c parallel to I) of (Tl, Hg)( 2)Ba2Ca2Cu3O10+delta (Tl 2223) and (Hg, Cu)Ba2CuO4+delta (Hg 1201) single c rystals has been measured. For Tl 2223, the observed change of sign in magn etoconductivity is explained in terms of density-of-states (DOS) fluctuatio ns and competition of this effect with the positive Aslamasov-Larkin contri bution. The mercury-based compound (Pig 1201) does not show such an anomaly . Indeed, in accordance with the theory, owing to its low anisotropy, this material shows a vanishing DOS contribution preventing any change of sign i n the experimental magnetoconductivity. Besides, the nature of the impurity state and the pair-breaking regime are discussed. [S0163-1829(99)03010-6].