Ultrasound Studies on the Chiral Antiferromagnet Mn₃Ge

The chiral antiferromagnet Mn₃Ge is a promising candidate for a magnetic Weyl semimetal, where Weyl nodes arise from broken time reversal symmetry rather than broken inversion symmetry. Recently, Mn₃Ge has been shown to exhibit a giant anomalous Hall effect at room temperature, which has been attributed to the presence of Weyl nodes. Given this highly anomalous room-temperature Hall effect, it is natural to ask whether other properties of the Weyl nodes, such as the chiral anomaly, are also present at room temperature. Strong magneto-elastic coupling, known to be present in Mn₃Ge, has motivated our investigation of the elastic moduli in this material. We report resonant ultrasound spectroscopy studies of the full elastic tensor of Mn₃Ge through the 380 K Néel transition temperature. We investigate how strains of different symmetry couple to the magnetic degrees of freedom on the Kagome lattice formed by manganese ions. We also investigate ultrasonic attenuation - which is predicted to be highly sensitive to chiral charge pumping between Weyl nodes in a magnetic field - both above and below the Néel transition.