First-principles prediction of strain-induced Dirac semimetal state and negative Poisson's ratio in TiZrB<inf>4</inf> monolayer

Abstract

In this work, we designed a novel 2D Dirac material, TiZrB4 monolayer, by transforming the hexagonal unit cells of the previously reported TiB2 and ZrB2 semimetals into an orthorhombic lattice. Using first-principles density functional theory (DFT) calculation, our designed 2D structure of TiZrB4 was verified to be dynamically and thermodynamically stable by phonon dispersion calculation and ab-initio molecular dynamics (AIMD). From the results, the TiZrB4 monolayer was found to be metallic with a maximum Fermi velocity (vF) of 0.409 × 106 m/s. By applying a uniaxial strain of 3.3% along the a-axis (the zigzag direction of the boron honeycomb), the TiZrB4 monolayer becomes a Dirac semimetal with an enhanced vF of 0.436 × 106 m/s. The electronic properties and vF were found to be tunable by external strain. In addition, the negative Poisson's ratio was found in the wide range of uniaxial strains due to strong transition metal d and boron p hybridization. We expect that our findings and 2D material design strategy will be suggestive and informative for the development of a new Dirac semimetal with superior properties useful in future nanotechnology.