超大型热电材料FeSb $_2$的电子和振动特性
Unusual electronic and vibrational properties in the colossal thermopower material FeSb$_2$
摘要：
锑化铁FeSb $_2$在低温下具有非常高的热电功率因数，使其成为低温热电冷却装置的主要候选者。然而，这种不寻常行为的起源是有争议的，已经被各种各样地归因于电子相关性以及声子拖曳效应。材料的光学性质提供了关于电子和振动性质的信息。的光学电导率揭示了在室温下的各向异性响应，低频光学电导率随温度迅速下降，信号的金属-绝缘体转变。在低温下沿$b$轴观察到一维半导体行为，与第一性原理计算一致。红外活性晶格振动也是对称的，并且非常窄，表明声子弛豫时间长，并且缺乏电子-声子耦合。令人惊讶的是，有更多的晶格模式沿$a$轴比从群论预测，这些模式中的几个发生显着变化低于约100 K，暗示在弱的结构畸变或相变。虽然极窄的声子线形状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有助于在该材料中观察到非常高的热电势。
英文摘要：
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.
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