XXXVI Reunión Bienal de la Real Sociedad Española de Física

A possible route towards superconductivity in layered nickelates

Not scheduled

Aula Magna (Santiago de Compostela, Facultade de Química)

Description

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.