Possible origin of the nonmonotonic doping dependence of the in-plane resistivity anisotropy of Ba(Fe1xTx)2As2 (T = Co, Ni and Cu)

The in-plane resistivity anisotropy has been measured for detwinned single crystals of Ba(Fe1-xNix)(2)As-2 and Ba(Fe1-xCux)(2)As-2. The data reveal a nonmonotonic doping dependence, similar to previous observations for Ba(Fe1-xCox)(2)As-2. Magnetotransport measurements of the parent compound reveal a nonlinear Hall coefficient and a large linear term in the transverse magnetoresistance. Both effects are rapidly suppressed with chemical substitution over a similar compositional range as the onset of the large in-plane resistivity anisotropy. This suggests that the relatively small in-plane anisotropy of the parent compound in the spin-density wave state is due to the presence of an isotropic, high mobility pocket of the reconstructed Fermi surface. Progressive suppression of the contribution to the conductivity arising from this isotropic pocket with chemical substitution eventually reveals the underlying in-plane anisotropy associated with the remaining Fermi surface pockets.