Superconductivity in (LuC)2(Ni2B2) and (LuC)(Ni2B2)

We have studied (LuC${)}_{2}$(${\mathrm{Ni}}_{2}$${\mathrm{B}}_{2}$) and (LuC)(${\mathrm{Ni}}_{2}$${\mathrm{B}}_{2}$) at ambient and high pressures. Superconductivity was discovered in (LuC${)}_{2}$(${\mathrm{Ni}}_{2}$${\mathrm{B}}_{2}$) at 2.9 K. Pressure was found to suppress both the electrical resistivity and the superconducting transition temperature rapidly for (LuC${)}_{2}$(${\mathrm{Ni}}_{2}$${\mathrm{B}}_{2}$) but only slightly for (LuC)(${\mathrm{Ni}}_{2}$${\mathrm{B}}_{2}$), in spite of their similar chemical-bonding behavior. The observations can be understood in terms of the smaller density of states at the Fermi surface and the greater pressure-induced band broadening of (LuC${)}_{2}$(${\mathrm{Ni}}_{2}$${\mathrm{B}}_{2}$) than (LuC)(${\mathrm{Ni}}_{2}$${\mathrm{B}}_{2}$).