MoS2, a member of transition metal dichalcogenides (TMDs), recently emerged as one of the fastest growing two-dimensional materials due to its fascinating mechanical, thermal, electronic and optical properties. Unlike graphene which possesses massless Dirac fermions with ultra-high electron mobility, monolayer MoS2 is a direct band gap semiconductor. An interesting question arises: Can monolayer MoS2 also possess massless Dirac fermions with ultra-high electron mobility? Here, using first-principles calculations, we show that a monolayer MoS2 allotrope, which consists of repeated square-octagon rings (abbreviated as so-MoS2 to distinguish from the normal hexagonal lattice, h-MoS2) possesses both massless Dirac fermions and heavy fermions. Distinct from the p-orbital Dirac fermions of graphene, the Dirac fermions of so-MoS2 are d-electrons and possess Fermi velocity comparable to that of graphene. The Dirac cone structure in so-MoS2 demonstrated here greatly enriches our understanding on the physical properties of TMDs and opens up new possibilities for developing novel electronic/spintronic devices.
@article{arxiv.1401.7721,
title = {A Gapless MoS$_2$ Allotrope Possessing Both Massless Dirac and Heavy Fermions},
author = {Weifeng Li and Meng Guo and Gang Zhang and Yong-Wei Zhang},
journal= {arXiv preprint arXiv:1401.7721},
year = {2015}
}