Enhanced Cryogenic Thermoelectricity in Semimetal Ta2PdSe6 through Non-Fermi Liquid-Like Charge and Heat Transport

The thermal properties of semimetal Ta₂PdSe₆ are studied, which exhibits a large thermoelectric power factor at low temperatures, by combining chemical substitution, transport measurements, and inelastic X-ray scattering. A serious violation of the Wiedemann-Franz law (WFL) is observed, which establishes the relationship between conductivity and thermal conductivity of metals. This violation leads to a thermal conductivity of Ta₂PdSe₆ lower than expected from the WFL and resistivity below 20 K, resulting in the highest figure of merit below 20 K among the p-type thermoelectric materials thus far. Furthermore, electric and thermal resistivity show a non-Fermi liquid-like temperature dependence, indicating an exotic electronic state with an unconventional scattering process for heat and charge carriers. This study suggests that semimetals in the non-Fermi liquid regime may be an intriguing platform, not only for fundamental physics but also for exploring novel thermoelectric materials tailored for low-temperature applications.