Topological flat bands for high-performance metallic thermoelectrics

Topological materials, where flattened electronic dispersions arise from destructive phase interference, rather than localized orbitals, are of immense current interest as they promise a rich tapestry of emergent correlation phenomena and novel physics to be discovered. Certain frustrated geometries such as the dice, Lieb, kagome or pyrochlore lattices are theoretically predicted to support completely flat bands. While various promising candidates have been identified and there are now even computational databases listing thousands of members, crucial next steps involve tuning such flat bands to the Fermi level and assessing how they manifest in the physical properties of the hosting materials.

Here, we propose that the interplay of highly dispersive and ultraflat bands inherent to these systems can lead to extreme interband scattering, which can be harnessed to design high-performance thermoelectrics [1,2]. Our comprehensive theoretical and experimental investigation of Ni₃In- and CoSn-based kagome metals supports this concept, showing that it could possibly lead to thermoelectric performance on par with state-of-the-art semiconductors such as Bi₂Te₃, the only commercial thermoelectric material since the mid-20th century.