Weak antilocalization in a noncentrosymmetric CaAgBi single crystal

TL;DR

This study investigates the weak antilocalization effect in the topological semimetal CaAgBi, combining experimental transport measurements with first-principles calculations to reveal its electronic structure and topological properties.

Contribution

It provides the first detailed experimental and theoretical analysis of weak antilocalization and topological Dirac semimetal states in CaAgBi single crystals.

Findings

Weak antilocalization observed below 100 K in CaAgBi.

CaAgBi supports a topological Dirac semimetal state with protected Dirac points.

Dominant p-type carriers confirmed by Hall measurements and Fermi surface analysis.

Abstract

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.