Alaska Subedi I Competing structural instabilities in infinite-layered rare-earth nickelates

Alaska Subedi, Ecole Polytechnique, Palaiseau

The recent reports of superconductivity in the infinite-layered rare-earth nickelates have generated great excitement because Ni ions in these materials have the same nominal valence as that of the Cu ions in the cuprate superconductors.  Hence, it has been suggested that the mechanism of superconductivity in these two families of compounds are similar, which is supported by theoretical studies taking into account their electronic structure and onsite Coulomb repulsion.  However, the full structural information of the infinite-layer nickelates, which is an essential ingredient to understand their physical properties, is still not known.  Previous first principles calculations have shown that the infinite-layer nickelates with smaller rare-earth ion exhibit structural instabilities that involve rotations and tilts of the NiO4 squares. In my talk, I discuss the results of my calculations that uncover further structural instabilities.  Furthermore, I find that several distorted structures lie very close in energy, suggesting that these materials lie near a structural quantum critical point.