Coexistence of Electronic and Phononic Dirac Points in TiB2 Monolayer with Inverse Sandwich Motif

Although many Dirac semimetals (DSMs) have been theoretically proposed, the ideal Dirac fermions coexisting with Dirac phonons in a DSM are rare. In this work, we proposed a general strategy to assemble two-dimensional (2D) ideal DSMs using the cluster of transition metal boride with an inverse sandwich configuration. We illustrated this strategy using firstprinciples calculations, resulting in the creation of a 2D titanium diboride named 2c-TiB2 with a space group of P21/c. This monolayer was found to be thermodynamically, dynamically, and thermally stable. Additionally, it was revealed to be a DSM with an ideal Dirac cone at the Fermi level, and its topology arises from the band inversion between the pz orbitals of B atoms and dx 2-y2 orbitals of Ti atoms. Furthermore, the monolayer exhibits intersecting Dirac phonons along high-symmetry path G-X. The quantized Berry phase, inversed eigenvalues, and apparent electronic and phononic topological edge states all served as further evidence of the topological protection originating from C2x symmetry. The theoretical investigation into inverse sandwich structured boride monolayer not only predicts the coexistence of Dirac fermions and Dirac phonons in 2D TiB2, but also provides a novel approach to design topological states in 2D nanomaterials.

Automated summary

In this study, a general strategy was proposed to assemble two-dimensional ideal Dirac semimetals using transition metal boride clusters. This strategy was illustrated by creating a thermodynamically stable 2D titanium diboride called 2c-TiB2, which was found to be a Dirac semimetal with an ideal Dirac cone at the Fermi level. Furthermore, this monolayer exhibited intersecting Dirac phonons.