High-resolution angle-resolved photoemission study of BaCo_1-xNi_xS₂

We have performed angle-resolved photoemission spectroscopy on a layered Mott system BaCo_1-x Ni_xS₂ across the phase transition from the antiferromagnetic insulator (x = 0.18) to anomalous metal (x = 0.28). In the anomalous metallic phase, we found a large Fermi surface centered at the M(A) point with a dominant Co (Ni) 3d_3z2^-r2 character. Hubbard bands in the insulating phase have a remnant of Fermi surface in the metallic phase and gradually evolve into metallic dispersive bands upon carrier doping. We conclude that the electronic structure of BaCo_1-xNi_xS₂ is basically different from that of the high-T_c cuprates although the transport and magnetic properties share some common features between the two layered compounds.