Single Crystal Growth And Planar Hall Effect Of Type-? Dirac Semimetal NiTe₂

Over the last decade,topological materials have developed rapidly in the field of condensed matter.From theoretical predictions of topological materials to experimental verification,a number of achievements have been made in this field and the rich topological materials provide versatile platforms for basic scientific research.During studying for Master's Degree,the author focused on the growth and magnetic transport of type-II Dirac semimetal,where the Dirac cone is strongly tilted along the certain direction because then fermion breaks the Lorentz invariance.The type-II Dirac point emerges at the contact of electron and hole pockets,so that the physical properties are distinct from type-I semimetals,such as Klein tunneling and an angle dependent chiral anomaly.The author's work is mainly based on a newly discovered type-II Dirac semimetal NiTe2 to study the origin of the planar Hall effect(PHE).We use the first-principles calculations to reveal the electronic structure of the NiTe2 and prove that this material is the type-II Dirac semimetal.The single crystals of NiTe2 were grown by the self-flux method.The results of X-ray diffraction(XRD)and the energy dispersive spectrum(EDS)indicate the high quality of the crystals.We research the de Haas-van Alphen oscillation and reveal the origin of different oscillation modes.We successfully observe the planar Hall effect(PHE)which is often attributed to the chiral anomaly of topological electrons.The planar Hall signals oscillate with the in-plane angle with a ? period and reach the extremum at 45°and 135°,which can be ideally described by the theoretical formulas.However,by analyzing the in-plane anisotropic magnetoresistance,there are not negative longitudinal magnetoresistance.In addition,the ?xx-?yx parametric plot exhibits a"shock-wave"pattern.We conclude that the PHE can be observed as long as the resistivity of a solid system is anisotropic when applying an in-plane magnetic field through mathematical derivation.All these evidences show that the presented PHE in NiTe2 originates from the trivial orbital magnetoresistance rather than the topological-nontrivial chiral anomaly.Our result can be taken as an example that the PHE is observed in topological materials but caused by a non-topological origin.In such studies,special attention is needed and one should take both orbital magnetoresistance and negative longitudinal magnetoresistance into consideration to distinguish the real origin of the PHE signals.