Multiple Dirac points including potential spin-orbit Dirac points in nonsymmorphic HfGe0.92Te.

The search for new materials with Dirac points has been a fascinating subject of condensed matter physics. Here we first report the growth and band structure of HfGe_0.92Te single crystals featuring three different types of Dirac points. HfGe_0.92Te crystallizes in a nonsymmorphic tetragonal space group P4/nmm (No. 129), having a square Ge-atom plane with vacancies of about 8%. Using angle-resolved photoemission spectroscopy (ARPES), the Dirac nodal line composed of conventional Dirac points vulnerable to spin-orbit coupling (SOC) is observed, accompanied by robust Dirac points protected by the nonsymmorphic symmetry against SOC and vacancies. In particular, spin-orbit Dirac points (SDPs) originating from the surface formed under significant SOC could exist based on ARPES and calculations. Quasi-two-dimensional (quasi-2D) characteristics are confirmed by angular-resolved magnetoresistance. HfGe_0.92Te bulk crystals can be easily exfoliated to flakes with a thickness of approximately 5 nm for the quasi-2D nature. Thus, HfGe_0.92Te provides a good platform to explore exotic topological phases or topological properties with three different types of Dirac points, which is a potential candidate to achieve novel 2D SDPs. [ABSTRACT FROM AUTHOR]