FLEET PhD student Weiyao Zhao
Intrinsic TIs are nonmagnetic or antiferromagnetic materials, possessing linear dispersed surface states with helical-textured spin configuration. With ferromagnetic ordering, a so-called massive Dirac state is achieved, in which the spin texture near Dirac gap is hedgehog like. Particularly, with fully spin polarization at Fermi surface, one can obtained the half-metallic TI, which should also exhibite the massive Dirac states, and potentially support the quantum anomalous Hall effect (QAHE).
To achieve this, here we present a co-doping strategy using synergistic rare-earth Sm and transition-metal Fe dopants in Bi2Se2 single crystals, which combine the advantages of both transition metal doped TI (high ferromagnetic ordering temperature and observed QAHE), and rare-earth doped TI (large magnetic moments and significant spin orbit coupling). In our codoped single crystals, magnetometry measurements reveal strong bulk ferromagnetic order involving Sm moments below 30 K, and a smaller residual magnetization that survives to 300 K which we assign to the role of surface Fe-impurities. Detailed transport experiments and angle resolve photoemission spectroscopy indicate the ferromagnetism opens a ~ 44 meV band gap at surface Dirac point.
Moreover, the carriers’ mobility at 3 K is ~ 8000 cm2/Vs, and we thus observed an ultra-strong Shubnikov-de Haas oscillation in the longitudinal resistivity, as well as the quantum Hall steps in transverse resistivity below 14 T. Based on ab-initial calculations, fully spin polarazition states at the Fermi surface are obtained, providing strong evidence of the half-metallic TI state.
About the presenter
Weiyao Zhao is a PhD student at the University of Wollongong, where he works with Prof Xiaolin Wang under Enabling technology A: atomically-thin materials and Research theme 1. Weiyao studies single-crystal growth of topological materials, via optical floating zone, slow cooling, and chemical vapor transport methods. His current focus is fabrication of high-quality topological insulator single crystals, as well as analysis of the crystal structure. Other areas of research include the transport properties of magnetic-doped topological insulators, and semimetals.