Single-crystal investigation of the 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 a noncentrosymmetric $I{4}_{1}md$ space group, in line with predictions of nontrivial topology. Magnetization, specific heat, and electrical transport measurements were used to confirm antiferromagnetic order below 5 K, with an estimated magnon excitation gap of $\mathrm{\ensuremath{\Delta}}=9.11$ K from heat capacity and hole-like carrier density of $1.4\ifmmode\times\else\texttimes\fi{}{10}^{20}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ 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 ${\ensuremath{\mu}}_{B}$/Ce is observed to occur below 30 kOe at 1.8 K in the $M(H)$ ($\mathbf{H}\ensuremath{\parallel}\mathbf{a}$) data. Small magnetic fields of 3 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 $\mathbf{H}\ensuremath{\parallel}\mathbf{a}$ and a simpler one for $\mathbf{H}\ensuremath{\parallel}\mathbf{c}$.