Homes C C, Du Q, Petrovic C, Brito W H, Choi S, Kotliar G
Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, New York, 11973, USA.
Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, New York, 11790, USA.
Sci Rep. 2018 Aug 3;8(1):11692. doi: 10.1038/s41598-018-29909-2.
The iron antimonide FeSb 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.
锑化铁（FeSb）在低温下具有极高的热电功率因数，使其成为低温热电冷却装置的主要候选材料。然而，这种异常行为的起源存在争议，有人将其归因于电子关联以及声子拖曳效应。材料的光学性质提供了有关电子和振动性质的信息。室温下的光导率显示出各向异性响应；低频光导率随温度迅速下降，这表明发生了金属-绝缘体转变。与第一性原理计算结果一致，在低温下沿b轴观察到一维半导体行为。红外活性晶格振动也是对称且极其狭窄的，这表明声子弛豫时间长且缺乏电子-声子耦合。令人惊讶的是，沿a轴的晶格模式比群论预测的更多；其中一些模式在约100 K以下会发生显著变化，这暗示着存在微弱的结构畸变或相变。虽然极其狭窄的声子线形有利于声子拖曳效应，但该系统在低温下的一维行为也可能导致这种材料中观察到的极高热电势。
