Title: Frustrated Superconductivity in the Trilayer Nickelate La$_4$Ni$_3$O$_{10}$

Abstract: 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$_4$Ni$_3$O$_{10}$ 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$_3$Ni$_2$O$_{7}$. 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 $s^\pm$-wave gap structures in La$_4$Ni$_3$O$_{10}$, 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.