Chemical Trend of Superconducting Transition Temperature in Hole-doped CuBO₂, CuAlO₂, CuGaO₂ and CuInO₂

We calculated the superconducting transition temperature $T_{\rm c}$ of hole-doped CuBO$_2$, CuAlO$_2$, CuGaO$_2$ and CuInO$_2$ using first-principles. The calculated $T_{\rm c}$ are about 50 K for CuAlO$_2$, 10 K for CuBO$_2$ and CuGaO$_2$ and 1 K for CuInO$_2$ at maximum in the optimum hole-doping concentration. The low $T_{\rm c}$ of CuInO$_2$ is attributed to the weak electron-phonon interaction caused by the low covalency and heavy atomic mass.