LaCo2B2: A Co-based layered superconductor with a ThCr2Si2-type structure

TL;DR

This paper reports the discovery of LaCo2B2, a layered superconductor with a ThCr2Si2-type structure, exhibiting superconductivity around 4K upon doping, with strong covalent Co-B bonding suppressing magnetic order.

Contribution

It introduces LaCo2B2 as a new Co-based layered superconductor with a ThCr2Si2-type structure and elucidates the role of covalent bonding in its superconductivity.

Findings

LaCo2B2 exhibits metallic conductivity and Pauli paramagnetism down to 2K.

Superconductivity with Tc ~4K is induced by doping with Y or Fe.

Strong covalent Co-B bonds suppress magnetic ordering in the material.

Abstract

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.