Antiferromagnetism driven charge density wave in infinite-layer NdNiO2 nickelates

One of the central issues concerning unconventional superconductivity is the nature of the charge-density-wave (CDW) order and its implication for the pairing mechanism. Recently, a CDW order has been discovered in undoped infinite-layer ${\mathrm{NdNiO}}₂$ nickelates, which cannot be explained by popular Fermi-surface-based mechanisms (such as Fermi surface nesting or strong electron-phonon coupling) due to the observed insulating behavior. In this paper, we investigate the CDW order in undoped ${\mathrm{NdNiO}}₂$ using first-principles calculations. We find that the CDW order formation is independent of the Fermi surface but is strongly correlated with the intrinsic antiferromagnetic (AFM) order. We propose a CDW mechanism based on enhancement of AFM coupling induced by symmetry reduction. We demonstrate that with the loss of fourfold rotational symmetry, the $\mathrm{Ni}\text{\ensuremath{-}}3{d}_{{x}²\ensuremath{-}{y}²}$ and $\mathrm{Nd}\text{\ensuremath{-}}5{d}_{{z}²}$ bonding establishes a Ni-Nd-Ni AFM superexchange channel. The AFM coupling between two adjacent Ni atoms in the same Ni-O plane is enhanced in the lower-symmetry CDW structure, making the CDW order energetically favorable and stabilized when the in-plane checkerboard AFM order is presented. Our findings suggest that AFM and lattice are strongly coupled in ${\mathrm{NdNiO}}₂$ nickelates, which provides inspiration for the origin of CDW order in other strongly correlated systems and for the elucidation of the mysterious pairing mechanism.