Observation of competing order in infinite-layer nickelates NdNiO2

Recently, the infinite-layer nickelates, which have similar crystal structure as cuprates, was successfully synthesized and exhibited superconductivity. Obviously, this new kind of Ni-based superconductors will create new platform to investigate the complex superconducting mechanisms in the cuprates. In the nickelates, there exist strong Coulomb interactions, which may result in different symmetry-breaking orders, like charge density waves (CDWs), spin density waves (SDWs). These orders may contribute to the superconductivity. Therefore, it's of importance to find out the possible ordered state in the nickelates. Here, we study the photoinduced change in reflectivity of the parent compound of the nickelate superconductor-NdNiO₂ films. Above 160 K, we observe an additional decay process, which coexist with the decay process at low temperature. At higher temperature, the second decay process dominate the relaxation. This phenomenon may reflect the existence of competing order in the temperature region in the NdNiO₂ film. Further efforts should be made to find out the physical origin of the orders.