  Superconducting nickelates are a new family of materials that combine
strongly-correlated magnetism with unconventional superconductivity. While
comparisons with the superconducting cuprates are natural, very little is known
about the metallic state of the nickelates, making these comparisons difficult.
We probe the electronic dispersion of thin-film superconducting 5-layer ($n=5$)
and metallic 3-layer ($n=3$) nickelates by measuring the Seebeck coefficient,
$S$. We find a temperature independent and negative $S/T$ for both the $n=5$
nickelate, with strange metal resistivity, and the $n=3$ compound, with more
conventional Fermi liquid resistivity. These results are in stark contrast with
the strongly temperature-dependent $S/T$ measured at similar electron filling
in the cuprate La$_{1.36}$Nd$_{0.4}$Sr$_{0.24}$CuO$_4$. We reproduce the
temperature dependence, sign, and amplitude of $S/T$ in the nickelates using
Boltzmann transport theory combined with the electronic structure calculated
from density functional theory. This demonstrates that the electronic structure
obtained from first-principles calculations is a good starting point for
calculating the transport properties of superconducting nickelates, and
suggests that, despite indications of strong electronic correlations, there are
well-defined quasiparticles in the metallic state of this family of materials.
Finally, we explain the differences in the Seebeck coefficient between
nickelates and cuprates as originating in strong dissimilarities in impurity
concentrations. Beyond establishing a baseline understanding of how the
electronic structure relates to transport coefficients in these new materials,
this work demonstrates the power of the semi-classical approach to
quantitatively describe transport measurements, even in the strange-metallic
state.
