Thermoelectric properties of 3D topological insulator: Direct observation of topological surface and its gap opened states
Thermoelectric properties of 3D topological insulator: Direct observation of topological surface and its gap opened states
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DOI：
10.1103/physrevmaterials.1.054202
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发表时间：
2017-03
期刊：
影响因子：
--
通讯作者：
S. Y. Matsushita;K. K. Huynh-K.;H. Yoshino;N. Tu;Y. Tanabe;K. Tanigaki
中科院分区：
文献类型：
--
作者：
S. Y. Matsushita;K. K. Huynh-K.;H. Yoshino;N. Tu;Y. Tanabe;K. Tanigaki
通过采用超薄外延生长的单晶Bi $_{2-x}$ Sb $_x$ TE $_{3-y}$ Se $_y$薄膜，我们报道了三维拓扑绝缘体（3D-TIs）中拓扑表面狄拉克态（TSDS）的热电（TE）性质。通过电输运，我们成功地观察到了金属TSDS （m-TSDS）和开隙半导体拓扑态（g-TSDS）这两个本征非简单表面拓扑态，并精确地确定了重要的TE参数（电导率（${\sigma}$）、导热系数（${\kappa}$）和热功率（$S$））。纯m-TSDS得到$S$ =-44 {\mu} VK $^{-1}$，比常规金属高一个数量级，g-TSDS得到-212 {\mu} VK $^{-1}$。结果清楚地表明，最常用于常规分析的恒定松弛时间（${\tau}$）框架下的半经典玻尔兹曼输移方程（SBTE）在3d - ti中是不成立的，而超越玻恩近似的强能量依赖的松弛时间${\tau}(E)$对于进行内在解释是必不可少的。虽然${\sigma}$在m-TSDS上受到保护，但${\kappa}$受到拓扑表面无序的极大影响，使得拓扑保护下的电子传导和声子输运的效果不同。
We report thermoelectric (TE) properties of topological surface Dirac states (TSDS) in three-dimensional topological insulators (3D-TIs) purely isolated from the bulk by employing single crystal Bi$_{2-x}$Sb$_x$Te$_{3-y}$Se$_y$ films epitaxially grown in the ultrathin limit. Two intrinsic nontrivial topological surface states, a metallic TSDS (m-TSDS) and a gap-opened semiconducting topological state (g-TSDS), are successfully observed by electrical transport, and important TE parameters (electrical conductivity (${\sigma}$), thermal conductivity (${\kappa}$), and thermopower ($S$)) are accurately determined. Pure m-TSDS gives $S$=-44 {\mu}VK$^{-1}$, which is an order of magnitude higher than those of the conventional metals and the value is enhanced to -212 {\mu}VK$^{-1}$ for g-TSDS. It is clearly shown that the semi-classical Boltzmann transport equation (SBTE) in the framework of constant relaxation time (${\tau}$) most frequently used for conventional analysis cannot be valid in 3D-TIs and strong energy dependent relaxation time ${\tau}(E)$ beyond the Born approximation is essential for making intrinsic interpretations. Although ${\sigma}$ is protected on the m-TSDS, ${\kappa}$ is greatly influenced by the disorder on the topological surface, giving a dissimilar effect between topologically protected electronic conduction and phonon transport.