Semi-Dirac semimetal in silicene oxide

Abstract

Semi-Dirac semimetal is a material exhibiting linear band dispersion in one direction and quadratic band dispersion in the orthogonal direction and, therefore, hosts massless and massive fermions at the same point in the momentum space. While a number of interesting physical properties have been predicted in semi-Dirac semimetals, it has been rare to realize such materials in condensed matters. Based on the fact that some honeycomb materials are easily oxidized or chemically absorb other atoms, here, we theoretically propose an approach of modifying their band structures by covalent addition of group-VI elements and strain engineering. We predict a silicene oxide with chemical formula of Si 2 O to be a candidate of semi-Dirac semimetal. Our approach is backed by the analysis and understanding of the effect of p-orbital frustration on the band structure of the graphene-like materials.2 Dirac Semimetals, as represented by graphene, have been intensively studied in the past decade as a condensed matter platform of massless Dirac fermions [1,2] . The electronic structure of graphene is characterized by two Dirac points, located at K and K', respectively, in the momentum space [3] . In a tight-binding (TB) picture, by tuning the nearest-neighbor hopping energies in a graphene lattice, as illustrated in Figure 1, the two Dirac points can approach each other and merge into one forming the so-called semi-Dirac point, near which the band dispersion exhibits a peculiar feature, i.e., being linear in one direction and quadratic in the orthogonal direction [4][5][6] . Materials possessing semi-Dirac points are called semi-Dirac semimetals, which provide a platform where massless and massive Dirac fermions coexist. Besides the apparent highly anisotropic transport properties [7] , a number of other interesting properties have been predicted for the semi-Dirac semimetals, such as distinct Landau-level spectrum in a magnetic field [8,9] , non-Fermi liquid [10] , Anderson localization [11] and Bloch-Zener oscillations [12] . It is therefore of great interest to search for materials realizing the semi-Dirac semimetals.While the TB picture provides important guidance, the search for semi-Dirac semimetals still relies on non-trivial materials design. A VO 2 /TiO 2 superlattice has been theoretically proposed to hold multiple semi-Dirac points within the first Brillouin zone (BZ) [13] . The formation mechanism of the semi-Dirac points in this material is described by a TB model [14] different from that illustrated in Figure 1. Recently, black phosphorus (BP) has been predicted to exhibit a single semi-Dirac point in the BZ under pressure [15] . An exciting experiment has shown that a giant Stark effect through electron doping on the surface of BP indeed yields a semi-Dirac point [16] , albeit at heavily n-type doped condition with the semi-Dirac point below the Fermi level by about 0.5 eV. A Dirac-to-semi-Dirac transition by merging two Dirac points, as illustrated in Figure 1, still remains 3 to be demonstrated in a solid-...

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