Ta4CoSi : A tantalum-rich superconductor with a honeycomb network structure

The crystal structure of solid-state materials with unique lattices is considered one of the main factors determining physical properties, including superconductivity. Materials with honeycomb lattices have inspired intense research interest for their novel properties. A previously unknown compound, ${\mathrm{Ta}}_{4}\mathrm{CoSi}$, is discussed herein, along with its crystal structure and superconducting properties. It crystallizes in a $\mathrm{Cu}{\mathrm{Al}}_{2}\text{\ensuremath{-}}\mathrm{type}$ structure (space group P4/mcc, No. 124), with the lattice parameters $a=b=6.17755(7)\phantom{\rule{0.16em}{0ex}}\AA{}$ and $c=4.98443(8)\phantom{\rule{0.16em}{0ex}}\AA{}$, featuring honeycomb networks of Ta-Ta in the (110) plane. Superconductivity is observed below the critical temperature of \ensuremath{\sim}2.45 K, while lower and upper critical magnetic fields are \ensuremath{\sim}9.86 mT and 0.84 T, respectively. Experiments and theoretical calculations show that the honeycomb lattices significantly influence the superconducting properties. This material may thus provide a new platform for investigating the exotic superconductivity of honeycomb networks.