Highly anisotropic type-II nodal line state in pure titanium metal

Abstract

A type-II nodal line state, along with its unique optical, magnetic, and transport properties, was theoretically proposed and experimentally evidenced quite recently. Here, based on first-principles calculations, we report that a pure Ti metal can serve as an excellent type-II nodal line material for experimental detection. In the Ti metal, the type-II nodal line situates in a quite large momenta region with a linear energy range larger than 1.5 eV. Its surface band is quite dispersive and thus is promising to be detected in a wide energy range. The position of the nodal line in the Ti metal can be flexibly tuned by applying uniaxial strain and elemental doping. Most interestingly, the band dispersions along the nodal line are highly anisotropic in three typical directions, and therefore, strong direction-dependent transport behavior can be expected. Our findings in the Ti metal are the first proposal of a highly anisotropic type-II nodal line state in elemental materials.