Single crystal investigation of proposed type-II Weyl semimetal CeAlGe

Abstract

We present details of materials synthesis, crystal structure, and anisotropic magnetic properties of single crystals of CeAlGe, a proposed type-II Weyl semimetal. Single-crystal x-ray diffraction confirms that CeAlGe forms in noncentrosymmetric I4${}_1$md space group, in line with predictions of non-trivial topology. Magnetization, specific heat and electrical transport measurements were used to confirm antiferromagnetic order below 5 K, with an estimated magnon excitation gap of $\hat{I}”$ = 9.11 K from heat capacity and hole-like carrier density of 1.44 $\times$ 10${}^{20}$ cm${}^{-3}$ from Hall effect measurements. The easy magnetic axis is along the [100] crystallographic direction, indicating that the moment lies in the tetragonal $ab$-plane below 7 K. A spin-flop transition to less than 1 $\hat{I}{¼}_B$/Ce is observed to occur below 30 kOe at 1.8 K in the $M(H)$ ($\mathbf{H}\Vert \mathbf{a}$) data. Small magnetic fields of 3 kOe and 30 kOe are sufficient to suppress magnetic order when applied along the $a$- and $c$-axes, respectively, resulting in a complex $T-H$ phase diagram for $\mathbf{H}\Vert \mathbf{a}$ and a simpler one for $\mathbf{H}\Vert \mathbf{c}$.