Unconventional density-wave state in Ruddlesden‒Popper nickelate La4Ni3O10

The recent discovery of superconductivity in Ruddlesden‒Popper (RP) nickelates Rn+1NinO3n+1 (R = rare earth) under high pressure provides a new platform to understand the underlying physics of high-temperature superconductivity. Previous transport measurements suggest a notable correlation between pressure-induced high-temperature superconductivity and a density-wave (DW) state. Therefore, identifying the nature of the DW state is a prerequisite for decoding the superconducting mechanism in the new family of high-temperature superconductors. Here, we report a comprehensive investigation of the ambient-pressure DW transition in high-quality La4Ni3O10 single crystals using 139La (I = 7/2) nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR). Our findings reveal a two-stage evolution of the DW order. Below T* ≈ 150 K, a short-range charge order develops in the inner Ni-O layer, accompanied by a dramatic enhancement of spin fluctuations. This is followed by a DW transition at TDW ≈ 133 K, establishing fully developed charge and spin orders across all Ni-O planes. The layer-dependent behaviour highlights that the mechanism of DW transitions in La4Ni3O10 may involve both the interlayer coupling and the electronic structure disparities between the inner and outer layers. These findings provide a new framework for understanding the complex DW state in RP nickelates and their potential role in high-temperature superconductivity. The authors reveal a two-stage formation of density-wave order in nickelate La4Ni3O10 at ambient pressure. First, a short-range charge order develops in the inner Ni-O layer, accompanied by a dramatic enhancement of spin fluctuations, followed by fully-developed charge and spin orders at lower temperature.