Topological properties in non-symmorphic BaNiS2: a path for tuning Rashba and Dirac bands

Relativistic effects in solids have attracted an increasing interest for they can induce non-trivial topological phases, such as spin-polarized electronic states, with promise for spintronics applications. One example is the splitting of bands with opposite spin polarization produced by the Rashba spin-orbit coupling in asymmetric potentials. Sizable splittings have been hitherto obtained using either heavy elements, where this coupling is intrinsically strong, or large surface electric fields.
In this talk, we give experimental evidence of very large Rashba splittings up to 0.15 eV in centrosymmetric BaNiS2. This unexpected result in the absence of electronically active heavy elements is explained by a huge staggered crystal field, which breaks inversion symmetry at the Ni site. We show that this mechanism of Rashba coupling amplification opens the possibility of tuning a spin current in the steady state, which would be promising for the development of spintronic devices. Finally, we shall discuss the intimate link between the non-symmorphic crystal structure of BaNiS2, responsible for a peculiar staggered structure of the spin texture of the Rashba bands, and the existence of non-trivial electronic states with Dirac-like energy dispersion.