Dr. Victor Pardo (Universidade de Santiago de Compostela)
The physics of superconducting cuprates has fascinated condensed matter physicists for decades. Apart from the recent reports on hydrogen-based compounds, they are still to date the materials with a highest recorded critical temperature. All the superconducting cuprates have in common (at least) the following features: i) a layered, quasi-two-dimensional structure with CuO2 building blocks, ii) the antiferromagnetic insulating nature of the parent compounds with a Cu2+:d9 oxidation state, iii) having the dx2-y2 as the active bands around the Fermi level, strongly hybridized with O-p states. Recently, the pursue of cuprate-like phases has been focusing mainly on iridates, their t2g-electron analogue with a square lattice formed with (pseudo)spin-a-half cations coupled antiferromagnetically. In principle, a direct comparison between nickelates and cuprates is tempting because Ni+ is formally isoelectronic with Cu2+. However, the well-known Ni+-layered compound LaNiO2 is a metal with broad eg bands crossing the Fermi level and a relatively small involvement of the O-p bands, that lie away from the Fermi level. Recently, a breakthrough in the search for low-valence nickelates was obtained by the synthesis and characterization of Pr4Ni3O8 (Pr438). This material shares many of the above cuprate-like features. It is a layered compound formed by NiO2 planes with the Ni cations arranged in a square lattice and an average valence close to 1+. In that situation, the x2-y2 band lies higher in energy, thus occupying the vicinity of the Fermi level. In addition, a strong hybridization with surrounding oxygens takes place (contrary to what happens in LaNiO2). Measurements show that Pr438 is a Fermi liquid with a nominal d-band filling that places it in the hole-overdoped regime of the cuprate phase diagram. Thus, doping this system with electrons is a plausible way of pursuing the appearance of superconductivity in this kind of layered nickelates. In this work, we present the study of possible electron-doping mechanisms on Pr438 and what effects these would have on its electronic structure. To this end, we have carried out ab initio density-functional-theory-based calculations, with the WIEN2k software, which uses the APW+lo method to solve the Kohn-Sham equations. We have carried out LDA+U calculations to deal with correlations in the Ni d manifold, a value of U= 7 eV was used for the calculations.
Dr. Antia S. Botana (Argonne National Laboratory)
Dr. Michael R. Norman (Argonne National Laboratory) Dr. Victor Pardo (Universidade de Santiago de Compostela)