Tailoring Dirac states in a correlated system by chemical substitution

In the vast domain of topological materials, the study of underlying mechanisms leading to the formation of nontrivial electronic band structures is key to discovering new topological electronic states [1]. In these systems, the control and manipulation of Dirac fermions also constitute a fundamental step toward the realization of novel electronic and spintronic devices.

By means of Angle-Resolved Photo-Emission Spectroscopy (ARPES) experiments and ab initio DFT calculations, we prove that it is possible to move and reshape massive Dirac nodal lines in reciprocal space in the correlated system BaCo_1−xNi_xS₂ by Co/Ni substitution [2]. We show that the underlying band-inversion mechanism is driven by a large d−p hybridization and electronic correlation combined with the nonsymmorphic symmetry of the crystal. Remarkably, the doping x via chemical substitution also controls the electronic phase diagram which features correlated d-electron Dirac states across its metallic phase.

Our results suggest that BaCo_1−xNi_xS₂ is a model system to effectively tailor correlated Dirac states. More generally, we show that the two standard features of correlated systems -that is, the hybrid d−p bands and the charge-transfer gap, constitute a promising playground to engineer Dirac and topological materials using chemical substitution or other macroscopic control parameters. Our present approach can be applied to a wide class of materials described by the d−p effective Hamiltonian.

[1] N. P. Armitage, E. J. Mele, A. Vishwanath, Rev. Mod. Phys. 90, 15001 (2018)

[2] N. Nilforoushan et al., PNAS 118, e2108617118 (2021)