Torque Magnetometry in GdBiPt and WTe\(_{2}\)

Abstract

Topological insulators have conducting surface states despite having an insulating bulk. Weyl semimetals are similar, except that they are robust against deformations. These classes of topological materials have recently generated much interest because of their topological descriptions and possible applications. We study in this thesis GdBiPt and WTe\(_{2}\), two semimetals that break inversion symmetry, anticipating Berry curvature on magnetism. We used torque magnetometry to precisely find magnetisations of GdBiPt due to external magnetic fields, demonstrating phase transitions. At lower temperatures for GdBiPt, we observed obvious deviation of non-monotonic magnetisation from a relatively linear shape below 12 K and the presence of a kink at various magnetic-field strengths, the latter of which allows us to determine a phase transition diagram with zero-field value consistent with prior results. In WTe\(_{2}\), we observed strange, out-of-phase low- and high-field behaviour that we have yet to be able to explain. The data are also consistent with diamagnetism. This is especially strange because WTe\(_{2}\) is a metallic material, which would require that it had small effective mass and strong spin-orbit coupling to be consistent. Finally, we found good quantum oscillation behaviour at various angles, which helps to map the Fermi surface, giving us greater insight into its band structure and possibly its material properties.