Specific heat of optimally doped Ba(Fe1-xTMx)2As2 (TM = Co and Ni) single crystals at low temperatures: A multiband fitting

Low temperature specific heat has been measured in optimally doped and highly overdoped nonsuperconducting Ba(Fe1-xTMx)(2)As-2 (TM = Co and Ni) single crystals. By using the data of the overdoped samples, we successfully removed the phonon contribution of the optimally doped ones, and derived the electronic specific heat coefficient gamma(e). Remarkably, we found a continuing temperature dependent gamma(e)(T) which follows the quadratic relation gamma(e) = gamma(0) + alpha T-2 in the low temperature limit. Together with the very small residual term gamma(0), linear magnetic field dependence of gamma(e), it is concluded that there are either small segments of nodal lines, or pointlike nodes in these samples.