Electronic Structure of Square-Planar Palladates

Nickelates have emerged as promising candidates for high-temperature superconductivity in recent years. By drawing analogies with the cuprates in terms of crystal structure and 3d electron count, superconductivity in nickelates was first discovered in the square-planar family with general formula R_n+1Ni_nO_2n+2(R = La, Pr, Nd), characterized by having n-NiO₂ layers and a Ni oxidation state close to 1+. Within this family, both the infinite-layer compound RNiO₂ (R = La, Pr, Nd) [1] and the quintuple-layer Nd₆Ni₅O₁₂ material [2] have been shown to be superconducting with similar critical temperature T_c ∼ 15 K. Motivated by this series of discoveries, we use first-principles calculations to construct the equivalent palladate series and compare it to the nickelate analogs both structurally and electronically. Our calculations show that the electronic structure of the Pd-compounds is closer to that of the cuprates as it displays a single-band d_x²-y² Fermi surface topology and a larger p-d hybridization than the corresponding Ni counterparts. These electronic features suggest that, if realized, reduced palladates could be promising candidates for higher-T_c superconductivity.

[1] Nature 572, 624 (2019)

[2] Nature Materials 21, 160 (2022)