Single crystal investigation of proposed type-II Weyl semimetal CeAlGe

TL;DR

This study synthesizes and characterizes single crystals of CeAlGe, confirming its noncentrosymmetric structure and antiferromagnetic order, and explores its magnetic phase diagram relevant to its proposed topological Weyl semimetal properties.

Contribution

It provides detailed structural, magnetic, and transport data on CeAlGe, supporting its classification as a type-II Weyl semimetal candidate with complex magnetic behavior.

Findings

CeAlGe has a noncentrosymmetric I4$_1$md structure.

Antiferromagnetic order occurs below 5 K.

Magnetic fields suppress magnetic order, revealing complex phase diagrams.

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 $\Delta$ = 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 $\it{ab}$-plane below 7 K. A spin-flop transition to less than 1 $\mu_B$/Ce is observed to occur below 30 kOe at 1.8 K in the $M(H)$ ($\bf{H}\|\bf{a}$) data. Small magnetic fields of 3 kOe and 30 kOe are sufficient to suppress magnetic order when applied along the $\it{a}$- and $\it{c}$-axes, respectively, resulting in a complex $\it{T-H}$ phase diagram for $\bf{H}\|\bf{a}$ and a simpler one for $\bf{H}\|\bf{c}$.