We use the coupled 2d-spin-3d-fermion model proposed by Rosch {\sl et. al.}
(Phys. Rev. Lett. {\bf 79}, 159 (1997)) to study the thermoelectric behaviour
of a heavy fermion compound when it is close to an antiferromagnetic quantum
critical point. When the low energy spin fluctuations are quasi two
dimensional, as has been observed in YbRh2Si2 and CeCu6−xAux, with a typical 2d ordering wavevector and 3d Fermi
surface, the ``hot'' regions on the Fermi surface have a finite area. Due to
enhanced scattering with the nearly critical spin fluctuations, the electrons
in the hot region are strongly renormalized. We argue that there is an
intermediate energy scale where the qualitative aspects of the renormalized hot
electrons are captured by a weak-coupling perturbative calculation. Our
examination of the electron self energy shows that the entropy carried by the
hot electrons is larger than usual. This accounts for the anomalous logarithmic
temperature dependence of specific heat observed in these materials. We show
that the same mechanism produces logarithmic temperature dependence in
thermopower. This has been observed in CeCu6−xAux. We
expect to see the same behaviour from future experiments on YbRh2Si2.Comment: RevTex, two-column, 7 pages, 2 figure