非中心对称CaAgBi单晶中的弱反定域
Weak antilocalization in a noncentrosymmetric CaAgBi single crystal
摘要：
本文报道了一种拓扑半金属CaAgBi的单晶生长和输运性质，该晶体具有六方$ABC-$型结构，空间群为非中心对称的$\mathit{P6_3mc}$（No.186）。在14 T的磁场和10 K下，电流在六方晶体结构的基面上的横向磁阻测量表明，I// [10-10]方向约为30%，I // [1-210]方向约为50%.磁电阻在低磁场区表现出尖点效应，表明在低于100 K的温度下存在弱的反定域效应。霍尔测量结果表明，主要的电荷载流子是$p$型表现出的线性行为的字段高达14 T，可以解释的基础上的单带模型。基于修正的Hikami-Larkin-Nagaoka（HLN）模型，对CaAgBi的磁导进行了分析。我们的密度泛函理论框架内的第一性原理计算表明，CaAgBi支持拓扑狄拉克半金属态的狄拉克点位于旋转轴上略高于费米能级，并受到$C_{6v}$点群对称性的保护。费米表面由电子袋和空穴袋组成。然而，空穴袋的尺寸比电子袋大得多，表明与我们的实验结果一致的占主导地位的$p$型载流子。
英文摘要：
We report on the single crystal growth and transport properties of a topological semimetal CaAgBi which crystallises in the hexagonal $ABC-$type structure with the non-centrosymmetric space group $\mathit{P6_3mc}$ (No. 186). The transverse magnetoresistance measurements with current in the basal plane of the hexagonal crystal structure reveal a value of about 30 % for I // [10-10] direction and about 50 % for I // [1-210] direction at 10 K in an applied magnetic field of 14 T. The magnetoresistance shows a cusp-like behavior in the low magnetic-field region, suggesting the presence of weak antilocalization effect for temperatures less than 100 K. The Hall measurements reveal that predominant charge carriers are $p$ type exhibiting a linear behavior for fields up to 14 T and can be explained based on the single band model. The magnetoconductance of CaAgBi is analysed based on the modified Hikami-Larkin-Nagaoka (HLN) model. Our first-principles calculations within a density-functional theory framework reveal that CaAgBi supports a topological Dirac semimetal state with Dirac points located on the rotational axis slightly above the Fermi level and are protected by $C_{6v}$ point-group symmetry. The Fermi surface consists of both the electron and hole pockets. However, the size of hole pockets is much larger than electron pockets suggesting the dominant $p$ type carriers in accord with our experimental results.
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