Experimental evidence for type-II Dirac semimetal in PtSe2

While a monolayer PtSe2 film is a semiconductor with interesting spin structure, bulk PtSe2 crystal has been predicted to be a topological Dirac semimetal that can host a newtype of Lorentz-violatingDirac fermions. Despite the intriguing predictions, experimental progress on the electronic structure of bulk PtSe2 has been hindered due to the lack of large, high-quality single-crystal samples. Here we report the growth and characterization of high-quality PtSe2 single crystals and reveal the electronic structure to provide direct evidence for the existence of three-dimensional type-II Dirac fermions. A comparison of the crystal, vibrational, and electronic structure to a related compound, PtTe2, is also discussed. Our work provides an important platform for exploring the novel quantum phenomena associated with type-II Dirac fermions in the 1T-PtSe2 class of transition-metal dichalcogenides.