Systematics of the temperature - dependent interplane resistivity in Ba ( Fe 1 − x Mx ) 2 As 2 ( M = Co , Rh , Ni , and Pd )

Temperature-dependent interplane resistivity ρc(T ) was measured systematically as a function of transitionmetal substitution in the iron-arsenide superconductors Ba(Fe1−xMx)2As2, M = Ni, Pd, Rh. The data are compared with the behavior found in Ba(Fe1−xCox)2As2, revealing resistive signatures of pseudogap. In all compounds we find resistivity crossover at a characteristic pseudogap temperature T ∗ from nonmetallic to metallic temperature dependence on cooling. Suppression of T ∗ proceeds very similarly in cases of Ni and Pd doping and much faster than in similar cases of Co and Rh doping. In cases of Co and Rh doping an additional minimum in the temperature-dependent ρc emerges for high dopings, when superconductivity is completely suppressed. These features are consistent with the existence of a charge gap covering part of the Fermi surface. The part of the Fermi surface affected by this gap is notably larger for Niand Pd-doped compositions than in Coand Rh-doped compounds.