High thermoelectric power factor through topological flat bands

TL;DR

This study demonstrates that tuning topological flat bands near the Fermi energy in kagome metals significantly enhances thermoelectric power factors, offering a new approach for efficient thermoelectric materials.

Contribution

It introduces the concept of engineering topological flat bands in kagome metals to boost thermoelectric performance, combining experimental and theoretical insights.

Findings

Achieved large power factors up to 5 mW/mK^2 at room temperature.

Tuning flat bands below the Fermi energy enhances the Seebeck coefficient.

Demonstrated the potential of topological flat bands as a new tuning mechanism.

Abstract

Thermoelectric (TE) materials are useful for applications such as waste heat harvesting or efficient and targeted cooling. While various strategies towards superior thermoelectrics through a reduction of the lattice thermal conductivity have been developed, a path to enhance the power factor is pressing. Here, we report large power factors up to 5 mW m$^{-1}$ K$^{-2}$ at room temperature in the kagome metal Ni$_3$In$_{1-x}$Sn$_x$. This system is predicted to feature almost dispersionless flat bands in conjunction with highly dispersive Dirac-like bands in its electronic structure around the Fermi energy $E_\text{F}$ [L. Ye et al., Nature Physics 1-5 (2024)]. Within this study, we experimentally and theoretically showcase that tuning this flat band precisely below $E_\text{F}$ by chemical doping $x$ boosts the Seebeck coefficient and power factor, as highly mobile charge carriers scatter into the flat-band states. Our work demonstrates the prospect of engineering extremely flat and highly dispersive bands towards the Fermi energy in kagome metals and introduces topological flat bands as a novel tuning knob for thermoelectrics.