Unusual electronic and vibrational properties in the colossal thermopower material FeSb${}_2$

Abstract

The iron antimonide FeSb${}_2$ possesses an extraordinarily high thermoelectric power factor at low temperature, making it a leading candidate for cryogenic thermoelectric cooling devices. However, the origin of this unusual behavior is controversial, having been variously attributed to electronic correlations as well as the phonon-drag effect. The optical properties of a material provide information on both the electronic and vibrational properties. The optical conductivity reveals an anisotropic response at room temperature; the low-frequency optical conductivity decreases rapidly with temperature, signalling a metal-insulator transition. One-dimensional semiconducting behavior is observed along the $b$ axis at low temperature, in agreement with first-principle calculations. The infrared-active lattice vibrations are also symmetric and extremely narrow, indicating long phonon relaxation times and a lack of electron-phonon coupling. Surprisingly, there are more lattice modes along the $a$ axis than are predicted from group theory; several of these modes undergo significant changes below about 100 K, hinting at a weak structural distortion or phase transition. While the extremely narrow phonon line shapes favor the phonon-drag effect, the one-dimensional behavior of this system at low temperature may also contribute to the extraordinarily high thermopower observed in this material.

arXiv comment7 pages with 5 figures and one table; 9 pages of supplementary material

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Cited by in corpus (7)

• Prediction of unconventional magnetism in doped FeSb2
• Predicting impurity spectral functions using machine learning
• Vacancy defect control of colossal thermopower in FeSb2
• Anisotropic Correlated Electronic Structure of Colossal Thermopower Marcasite FeSb${}_2$
• Optical conductivity and vibrational spectra of the narrow-gap semiconductor FeGa${}_3$
• Anisotropic Surface State Band Splitting and Low Energy Flat Bands in 3d Correlated Topological Kondo Insulator Candidate FeSb${}_2$
• Prototypical many-body signatures in transport properties of semiconductors