Design principles for topological thermoelectrics

Conventional metals, insulators, and semimetals are constrained by fundamental limitations in terms of their thermoelectric performance. Topological materials offer certain features that allow them to circumvent these constraints, and potentially to form the basis for thermoelectric devices with unprecedented efficiency. In this article we review the thermoelectric performance of topological materials, focusing specifically on nodal semimetals, such as Weyl and nodal-line semimetals. We discuss how certain unique "topological" features of these materials -- namely their topologically protected band touching points, electron-hole degenerate lowest Landau level, and Berry curvature -- allow them to exhibit thermoelectric properties that go beyond what is possible in conventional materials, particularly in the presence of an applied magnetic field. We focus our discussion on the goal of achieving large figure of merit zT, and for each material class we summarize optimal design principles for selecting materials that maximize thermoelectric efficiency. We then use these optimal design principles to design and implement a high-throughput database search for topological semimetals that are promising as thermoelectrics. In addition to highlighting a number of materials that are already known to have large magnetothermoelectric effects, our search uncovers twelve additional materials that are especially promising for near-future experiments.