  Temperature dependent thermoelectric power (TEP) data on Ba(Fe1-xTMx)2As2 (TM
= Co and Cu), complemented by the Hall coefficient data on the samples from the
same batches, have been measured. For Co-doping we clearly see a change in the
temperature dependent TEP and Hall coefficient data when the sample is doped to
sufficient $e$ (the number of extra electrons associated with the TM doping) so
as to stabilize low temperature superconductivity. Remarkably, a similar change
is found in the Cu-doped samples at comparable e-value, even though these
compounds do not superconduct. These changes possibly point to a significant
modification of the Fermi surface / band structure of Ba(Fe1-xTM_x)2As2 at
small electron doping, that in the case of Co-doping is just before, and
probably allows for, the onset of superconductivity. These data further suggest
that suppression of the structural / magnetic phase transition and the
establishment of a proper e-value are each necessary but, individually, not
sufficient conditions for superconductivity.
