Probing of the pseudogap via thermoelectric properties in the Au-Al-Gd quasicrystal approximant
Probing of the pseudogap via thermoelectric properties in the Au-Al-Gd quasicrystal approximant
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DOI：
10.1103/physrevb.95.104201
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发表时间：
2017-03-06
影响因子：
3.7
通讯作者：
Tamura, Ryuji
中科院分区：
文献类型：
--
作者：
Ishikawa, Asuka;Takagiwa, Yoshiki;Tamura, Ryuji
利用热电性质作为实验探针，研究了最近发现的Au-Al-Gd准晶近似晶体（AC）在近似于0.5的宽电子/原子（e/a）比下的赝隙。这种Au-Al-Gd AC提供了一个理想的平台，用于在许多已知的AC中精细探测赝隙，因为Au-Al-Gd AC具有相对于电子浓度变化的非常宽的单相区域[a . Ishikawa， T. Hiroto， K. Tokiwa， T. Fujii, and R. Tamura, Phys]。Rev. B 93, 024416(2016)]，与二元化学计量Cd6R ACs形成鲜明对比。因此，除了电导率σ和S的逐渐变化外，在塞贝克系数S和功率因数S-2 sigma的组成中观察到一个显著的峰结构，这两个特征分别与光谱电导率S (E)的快速和缓慢变化直接相关，因此在费米能级EF附近的赝隙内部有精细结构。基于先前实验中观测到的费米波矢量的连续变化，尝试将EF微调到最优位置，成功地观测到S-2 sigma的一个尖峰，其值接近270 mu W/m。K-2在873 K。这是迄今为止在tsai型和bergman型化合物中报道的最高值。在873 K时，无因次优值为0.026，这也是在tsai型和bergman型化合物中报道的最高值。
The pseudogap of the recently discovered Au-Al-Gd quasicrystal approximant crystal (AC) is investigated over a wide electron-per-atom (e/a) ratio of similar to 0.5 using thermoelectric properties as an experimental probe. This Au-Al-Gd AC provides an ideal platform for fine probing of the pseudogap among a number of known ACs because the Au-Al-Gd AC possesses an extraordinarily wide single-phase region with respect to the variation in the electron concentration [ A. Ishikawa, T. Hiroto, K. Tokiwa, T. Fujii, and R. Tamura, Phys. Rev. B 93, 024416 (2016)], in striking contrast to, for instance, binary stoichiometric Cd6R ACs. As a result, a salient peak structure is observed in the Seebeck coefficient, S, with the composition as well as that of the power factor S-2 sigma, in addition to a gradual variation in the conductivity, sigma, and S. These two features are directly associated with rapid and slow variations, respectively, of spectral conductivity s(E), and hence the fine structure inside the pseudogap, in the vicinity of the Fermi level EF. Based on the observed continuous variation of the Fermi wave vector reported in the previous experimental work, fine tuning of EF toward an optimal position was attempted, which led to the successful observation of a sharp peak in S-2 sigma with a value of similar to 270 mu W/m . K-2 at 873 K. This is the highest value ever reported among both Tsai-type and Bergman-type compounds. The dimensionless figure of merit was determined as 0.026 at 873 K, which is also the highest reported among both Tsai-type and Bergman-type compounds.