Thermopower of the Correlated Narrow Gap Semiconductor FeSi and Comparison to RuSi
Iron based narrow gap semiconductors such as FeSi, FeSb2, or FeGa3have received a lot of attention because they exhibit a large thermopower, as well as striking similarities to heavy fermion Kondo insulators. Many proposals have been advanced, however, lacking quantitative methodologies applied to this problem, a consensus remained elusive to date. Here, we employ realistic many-body calculations to elucidate the impact of electronic correlation effects on FeSi. Our methodology accounts for all substantial anomalies observed in FeSi: the metallization, the lack of conservation of spectral weight in optical spectroscopy, and the Curie susceptibility. In particular, we find a very good agreement for the anomalous thermoelectric power. Validated by this congruence with experiment, we further discuss a new physical picture of the microscopic nature of the insulator-to-metal crossover. Indeed, we find the suppression of the Seebeck coefficient to be driven by correlation induced incoherence. Finally, we compare FeSi to its iso-structural and iso-electronic homologue RuSi, and predict that partially substituted Fe1 − x Ru x Si will exhibit an increased thermopower at intermediate temperatures.
KeywordsThermoelectric Property Seebeck Coefficient Spectral Weight Thermoelectric Performance Electronic Correlation Effect
We thank F. Steglich, P. Sun, and S. Paschen for stimulating discussions. JMT further acknowledges IICAM travel support through the NATO advanced workshop “The New Materials for Thermoelectric Applications: Theory and Experiment” in Hvar, as well as the hospitality at MPI CPfS, Dresden. The authors were supported by the NSF-materials world network under grant number NSF DMR 0806937 and NSF DMR 0906943, and by the PUF program. Acknowledgment is also made to the donors of the American Chemical Society Petroleum Research Fund 48802 for partial support of this research.
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