Frustrated Superconductivity in the Trilayer Nickelate La_4Ni_3O_10

Motivated by the opposite trend of maximum T_c in multilayer nickelate and cuprate superconductors, we propose an interlayer pairing scenario for the superconductivity of the trilayer nickelate La_4Ni_3O_10 discovered recently under high pressure. Our theory reveals intrinsic frustration of the spin-singlet pairing formed between two outer layers and the same inner layer, which causes strong superconducting fluctuations between layers and thus explains the reduction of its maximum T_c compared to that of the bilayer La_3Ni_2O_7. This supports a fundamental distinction between multilayer nickelate and cuprate superconductors associated with their potentially different (interlayer vs intralayer) pairing mechanisms. Our theory predicts extended s^±-wave gap structures in La_4Ni_3O_10, with varying signs and possible nodes on different Fermi pockets. We also find an intrinsic Josephson coupling with potentially interesting consequences to be examined in future experiments.