Quantum oscillation measurements of a type-II Weyl semimetal

Type-II Weyl semimetals, characterized by strongly tilted Weyl cones, exhibit attractive properties for applications such as room-temperature optoelectronics and photodetectors. Unlike their type-I counterparts, these materials do not respect Lorentz symmetry and have Weyl nodes that act as the contact points between electron and hole pockets in the Fermi surface.

Hu et al. performed quantum oscillation studies of LaAlGe, a type-II Weyl semimetal, in order to map the Fermi surface of this unique material. They found that electronic transport is dominated by Weyl nodes with very small effective masses and high Fermi velocities. In addition, they observed possible quasi-2D Fermi surface sheets in 3D semimetals, which, when integrated with a magnetic rare-earth element such as cerium or praseodymium, could provide spin-polarized currents.

The researchers grew single crystals of LaAlGe using a high temperature self-flux method. Temperature- and angular-dependent de Haas-van Alphen oscillations were measured at the National High Magnetic Field Laboratory. Data analysis revealed quasiparticle masses smaller and Fermi velocities much larger than those of other Weyl semimetals such as SrMnBi₂ and WTe₂.

They observed three main frequencies, with the angular dependence of two frequencies being well-fitted by a 2D model, despite the absence of 2D structural features such as van der Waals bonds. This finding suggests that, by replacing lanthanum with a magnetic element such as cerium or praseodymium, these conducting states could provide spin-polarized Dirac currents.

The group is currently investigating the magnetic properties of similar materials in collaboration with scientists at synchrotron and neutron scattering facilities.

Source: “High Fermi velocities and small cyclotron masses in LaAlGe,” by Zhixiang Hu, Qianheng Du, Yu Liu, D. Graf, and C. Petrovic, Applied Physics Letters (2020). The article can be accessed at http://doi.org/10.1063/5.0035445 .