Unconventional magnetoresistance and electronic transition in Mn3Ge Weyl semimetal

Weyl semimetals are well known for their anomalous transport effects caused by a large fictitious magnetic field generated by the nonzero Berry curvature. We performed the analysis of the electrical transport measurements of the magnetic Weyl semimetal ${\mathrm{Mn}}₃\mathrm{Ge}$ in the a-b and a-c planes. We have observed negative longitudinal magnetoresistance (LMR) at a low magnetic field ($B<1.5$ T) along all the axes. The high-field LMR shows different behavior along the $x$ 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. The 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 ${\mathrm{Mn}}₃\mathrm{Ge}$ is driven by the metallic-semimetallic nature of the compound and (ii) ${\mathrm{Mn}}₃\mathrm{Ge}$ 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.