LaCo2B2 with a ThCr2Si2-type structure composed of alternately stacked La and CoB layers exhibits metallic electrical conductivity and Pauli paramagnetic behavior down to 2K. Bulk superconductivity with a Tc of ~4K emerges upon substitution with dopant elements; i.e., isovalent substitution to form (La1-xYx)Co2B2, or aliovalent substitution to form La(Co1-xFex)2B2. Highly covalent bonding between Co 3d and B 2p levels in the CoB layers, which is caused by the B 2p level being shallower than the Fermi level, removes magnetic ordering from Co 3d electrons even in the undoped samples.
@article{arxiv.1103.0597,
title = {LaCo2B2: A Co-based layered superconductor with a ThCr2Si2-type structure},
author = {Hiroshi Mizoguchi and Toshiaki Kuroda and Toshio Kamiya and Hideo Hosono},
journal= {arXiv preprint arXiv:1103.0597},
year = {2015}
}