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 As2 (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 ye. Remarkably, we found a continuing temperature dependent &ggr;e(T) which follows the quadratic relation &ggr;e = &ggr;0 + αT2 in the low temperature limit. Together with the very small residual term &ggr;0, linear magnetic field dependence of &ggr;e, it is concluded that there are either small segments of nodal lines, or pointlike nodes in these samples. [ABSTRACT FROM AUTHOR]