First-Principles Study of Hole-Doped Superconductors RNiO_2 (R = Nd, La, and Pr)

Recent experiments have found that in contrast to the nonsuperconducting bulk RNiO_2 (R = Nd, La, and Pr), the strontium-doped R_1-xSr_xNiO_2 thin films show superconductivity with the critical temperature T_\rm c of 9–15 K at x=0.2, whose origin of superconductivity deserves further investigation. Based on first-principles calculations, we study the electronic structure, lattice dynamics, and electron–phonon coupling (EPC) of the undoped and doped RNiO_2 (R = Nd, La, and Pr) at the experimental doping level. Our results show that the EPC-derived T_\rm c's are all about 0 K in the undoped and doped RNiO_2. The electron–phonon coupling strength is too small to account for the observed superconductivity. We hence propose that the electron–phonon interaction can not be the exclusive origin of the superconductivity in RNiO_2 (R = Nd, La, and Pr).