  The search for materials with large thermopower is of great practical
interest. Dirac and Weyl semimetals have recently proven to exhibit superior
thermoelectric properties, particularly when subjected to a quantizing magnetic
field. Here we consider whether a similar enhancement arises in nodal line
semimetals, for which the conduction and valence band meet at a line or ring in
momentum space. We compute the Seebeck and Nernst coefficients for arbitrary
temperature and magnetic field and we find a wealth of different scaling
regimes. Most strikingly, when a sufficiently strong magnetic field is applied
along the direction of a straight nodal line or in the plane of a nodal ring,
the large degeneracy of states leads to a large, linear-in-$B$ thermopower that
is temperature-independent even at low temperatures. Our results suggest that
nodal line semimetals may offer significant opportunity for efficient,
low-temperature thermoelectrics.
