Electronic structure and physical properties of the candidate topological material GdAgGe

Abstract

We grew needle-shaped single crystals of GdAgGe, which crystallizes in a noncentrosymmetric hexagonal crystal structure with space group $P\overline{6}$ $2m$ (189). The magnetic susceptibility data for $H \ensuremath{\perp} c$ reveal two pronounced antiferromagnetic transitions at ${T}_{N1}$ = 20 K and ${T}_{N2}$ = 14.5 K. The magnetic susceptibility anomalies are less prominent for $H \ensuremath{\parallel} c$. The transition at ${T}_{N1}$ is accompanied by a pronounced heat capacity anomaly confirming the bulk nature of the magnetic transition. Below ${T}_{N1}$, the electrical resistivity data follows a ${T}^{3/2}$ dependence. In the magnetically ordered state, GdAgGe shows positive transverse magnetoresistance, which increases with decreasing temperature and increasing field, reaching a value of $\ensuremath{\sim}27%$ at 9 T and 10 K. The Hall resistivity data and electronic band structure calculations suggest that both the hole and the electron charge carriers contribute to the transport properties. The electronic band structure displays linear band crossings near the Fermi level. The calculations reveal that GdAgGe has a nodal line with drumhead surface states coupled with a nonzero Berry phase, making it a nontrivial nodal-line semimetal.