Large Spin Hall Conductivity and Excellent Hydrogen Evolution Reaction Activity in Unconventional PtTe _1.75 Monolayer

Two-dimensional (2D) materials have gained lots of attention due to the potential applications. In this work, we propose that based on first-principles calculations, the (2 × 2) patterned PtTe 2 monolayer with kagome lattice formed by the well-ordered Te vacancy (PtTe 1.75 ) hosts large and tunable spin Hall conductivity (SHC) and excellent hydrogen evolution reaction (HER) activity. The unconventional nature relies on the A 1 @ 1 b band representation of the highest valence band without spin–orbit coupling (SOC). The large SHC comes from the Rashba SOC in the noncentrosymmetric structure induced by the Te vacancy. Even though it has a metallic SOC band structure, the ℤ 2 invariant is well defined because of the existence of the direct bandgap and is computed to be nontrivial. The calculated SHC is as large as 1.25 × 10 3 ℏ e (Ω cm) −1 at the Fermi level ( E F ). By tuning the chemical potential from E F − 0.3 to E F + 0.3 eV, it varies rapidly and monotonically from −1.2 × 10 3 to 3.1 × 1 0 3 ℏ e Ω cm − 1 . In addition, we also find that the Te vacancy in the patterned monolayer can induce excellent HER activity. Our results not only offer a new idea to search 2D materials with large SHC, i.e., by introducing inversion–symmetry breaking vacancies in large SOC systems, but also provide a feasible system with tunable SHC (by applying gate voltage) and excellent HER activity.