The Effect of Pressure on the Electronic and Crystal Structure in the La_n+1Ni_nO_3n+1 Family and Superconductivity in La₃Ni₂O₇

The recent discovery of superconductivity in the infinite layer nickelates ⁽¹⁾ has reanimated the search for superconductivity in nickelates, with a new upsurge after the discovery of superconductivity in La₃Ni₂O₇ at relatively high temperature at applied pressure^(2-3). Motivated by this, we study multiple related Ruddlesden–Popper (RP) oxide phases to understand the coupled electronic and crystal structure transition leading to superconductivity in multiple layered materials. We will present a detailed study on the effect of pressure on the structural, electronic, and magnetic properties of this materials class. We focus here on two key members of the La_n+1Ni_nO_3n+1 series namely La₃Ni₂O₇(both the bilayer and monolayer-trilayer polymorphs) and La₄Ni₃O₁₀ (a trilayer system, for which we analyse multiple polymorphs). In agreement with the experiment, our first principles calculation showed that around ~15 GPa pressure the orthorhombic (monoclinic)-to-tetragonal transition takes place for most of these polymorphs, coupled to an electronic transition.<br/>In addition to the electronic structure, we explore the effect of electronic correlations Hubbard parameter (U_eff) and pressure on this materials family. We observe a competition between the U_effand the pressure on the magnetic moment, finding that a low U is key to allowing for the dimerization and structural transition allowing for superconductivity. Thus, in this work, we will provide further insight into the coupled electronic and crystal structure coupling relating these materials under pressure, which may underlie the already observed superconducting transition in La₃Ni₂O_7.<br/><br/>References:<br/>1. Li, D., Lee, K., Wang, B.Y., Osada, M., Crossley, S., Lee, H.R., Cui, Y., Hikita, Y. and Hwang, H.Y., 2019. Superconductivity in an infinite-layer nickelate. Nature, 572(7771), pp.624-627.<br/>2. Sun, H., Huo, M., Hu, X., Li, J., Liu, Z., Han, Y., Tang, L., Mao, Z., Yang, P., Wang, B. and Cheng, J., 2023. <i>Nature</i>, <i>621</i>(7979), pp.493-498.<br/>3. Hosoya, T., Igawa, K., Takeuchi, Y., Yoshida, K., Uryu, T., Hirabayashi, H. and Takahashi, H., 2008, July. <i>Journal of Physics: Conference Series</i> (Vol. 121, No. 5, p. 052013).