Tuning Dirac nodes with correlated d-electrons in BaCo_(1-x)Ni_(x)S₂

Dirac fermions play a central role in the study of topological phases, for they can generate a variety of exotic states, such as Weyl semimetals and topological insulators. The control and manipulation of Dirac fermions constitute a fundamental step towards the realization of novel concepts of electronic devices and quantum computation. By means of ARPES experiments and ab initio simulations, here we show that Dirac states can be effectively tuned by doping a transition metal sulfide, BaNiS2, through Co/Ni substitution. The symmetry and chemical characteristics of this material, combined with the modification of the charge transfer gap of BaCo_{1-x}Ni_{x}S_{2} across its phase diagram, lead to the formation of Dirac lines whose position in k-space can be displaced along the Gamma M symmetry direction, and their form reshaped. Not only does the doping x tailor the location and shape of the Dirac bands, but it also controls the metal-insulator transition in the same compound, making BaCo_{1-x}Ni_{x}S_{2} a model system to functionalize Dirac materials by varying the strength of electron correlations.