UC Santa Barbara

Heusler compounds are a large family of ternary intermetallic compounds with more than 1500 predicted members across a large fraction of the periodic table [1]. They have been previously shown to exhibit novel electronic and magnetic behaviors such as half-metallic ferromagnetism [2], superconductivity [3], semiconductivity [4], and topologically non-trivial surface states [5]. Recent theoretical predictions [6,7] suggest the presence of time-reversal breaking Weyl and nodal line semimetallic behaviors in full-Heusler half-metallic Co2TiGe and Co2TiSn. In this work, the study of Weyl semimetallic half-metal Co2TiSn thin film was grown using Molecular Beam Epitaxy. A method of Fermi level tuning by substituting Co with Ni element was applied in order to bring the Fermi level toward the Weyl point to observe the signature of the Weyl semimetallic behavior in this system. The electronic structure of the Co2TiSn, the effect of Fermi level tuning using Ni alloying, and the probing of any signatures of Weyl semimetallicity in Co2TiSn were examined by angle-resolved photoemission spectroscopy, electrical, and magnetotransport measurement. In the second part of the study, the Fermi level tuning is used for the half-metal half Heusler PtMnSb, which has been seen as a promising material for spintronics application with inversion broken symmetry and large spin-orbit coupling, in order to further investigate the interplay of non-trivial band topology and magnetism within this system. The PtMnSb thin film was grown using Molecular Beam Epitaxy. Similar to that of Co2TiSn, the effect of Fermi level tuning by substituting Mn with Lu element to close the band gap was examined using X-ray diffraction and transport measurement to realize if a potential band inversion/Weyl point formation can form during the topological phase transition from a half metal to a topological insulator through Lu alloying.