Kane Fermion in a Two-Dimensional π-Conjugated Bis(iminothiolato)nickel Monolayer.

Massless Kane fermions revealed in zinc-blende semiconductors have recently gained interest in the broad study of relativistic materials. In particular, two-dimensional (2D) Kane fermions were expected to be hybrids of pseudospin-1 and -1/2 Dirac fermions. Based on first-principles calculations, we demonstrated that 2D Kane fermions can be realized in a recently synthesized metal-organic framework, namely, bis(iminothiolato)nickel monolayer. A slight compression takes the system from a semimetal to a semiconductor. At the critical strain of ∼1%, the upper and lower conical bands linearize and touch at a single point intersecting a flat band, showing the same dispersion as the pseudospin-1 Dirac-Weyl systems. We adopted a tight-binding Hamiltonian of a line-centered honeycomb lattice to reveal the origins and topology of the electronic band structure. The coexistence of Kane-type and Dirac-type spectra in the bis(iminothiolato)nickel monolayer is expected to benefit the study of multi quasiparticle effects.