Unconventional magneto-resistance, and electronic transition in Mn$_3$Ge Weyl semimetal

TL;DR

This study investigates the electronic and magneto-resistive properties of Mn$_3$Ge Weyl semimetal, revealing a temperature-driven topological transition and complex high-field magneto-resistance behavior linked to its electronic structure.

Contribution

It uncovers a temperature-induced electronic band transition near 200 K and links it to lattice parameter changes, advancing understanding of transport phenomena in magnetic Weyl semimetals.

Findings

Negative longitudinal magneto-resistance at low fields along all axes.

High field LMR behavior differs along x and z axes and changes near 200 K.

Electronic band topological transition occurs near 200 K.

Abstract

Weyl semimetals are well known for their anomalous transport effects caused by a large fictitious magnetic field generated by the non-zero Berry curvature. We performed the analysis of the electrical transport measurements of the magnetic Weyl semimetal Mn$_{3}$Ge in the a-b and a-c plane. We have observed negative longitudinal magneto-resistance (LMR) at a low magnetic field ($B<1.5$ T) along all the axes. The high field LMR shows different behavior along x and z axes. A similar trend has been observed in the case of planar Hall effect (PHE) measurements as well. The nature of high field LMR along the x axis changes near 200 K. Dominant carrier concentration type, and metallic to semimetallic transition also occur near 200 K. These observations suggest two main conclusions: (i) The high field LMR in Mn$_3$Ge is driven by the metallic - semimetallic nature of the compound. (ii) Mn$_3$Ge compound goes through an electronic band topological transition near 200 K. Single crystal neutron diffraction does not show any change in the magnetic structure below 300 K. However, the in-plane lattice parameter (a) shows a maximum near 230 K. Therefore, it is possible that the change in electronic band structure near 200 K is driven by the a lattice parameter of the compound.