Electronic structure of nickelates: From two-dimensional heterostructures to three-dimensional bulk materials

Abstract

Reduced dimensionality and strong electronic correlations, which are among the most important ingredients for cuprate-like high-Tc superconductivity, characterize also the physics of nickelate based heterostructures. Starting from the local density approximation we arrive at a simple twoband model for quasi two-dimensional (2D) LaNiO3/LaAlO3 heterostructures and extend it by introducing an appropriate hopping in the z direction to describe the dimensional crossover to three dimensions (3D). Using dynamical mean field theory, we study the effects of electronic correlations with increasing interaction strength along the crossover from 2D to 3D. Qualitatively, the effects of electronic correlations are surprisingly similar, albeit quantitatively larger interaction strengths are required in three dimensions for getting a Mott-Hubbard insulating state. The exchange parameters of an effective Kugel-Khomskii-like spin-orbital-model are also derived and reveal strong antiferromagnetic tendencies.

Orbital polarization in strainedLaNiO3: Structural distortions and correlation effects

“…As noted in the introduction, DMFT calculations performed using the very different framework of a low-energy description involving only e g states (defined, e.g., from an EW basis) found a large enhancement of the OP by corre- lation effects. 21,22 This raises the important question of what is the appropriate minimal low-energy model for nickelates, 29 a question that is beyond the scope of the present paper but which we intend to return to in future work.…”

“…Further progress in the field aiming at achieving larger or even full orbital polarization 19,21,22 will have to overcome these effects by considering appropriate materials and heterostructures.…”

“…The key question is whether conditions can be found such that this OP is large and the quasi two-dimensional d x 2 −y 2 band is a dominantly occupied one with proper filling. This issue was previously investigated by Hansmann et al 21,22 and Han et al, 23 for LaNiO 3 /LaAlO 3 heterostructures, and proposals for achieving high OP by using other LNObased heterostructures [24][25][26][27] or chemical control by other counterions 28,29 were made.…”

“…30,31 In the work of Hansmann et al, 21,22 a low-energy description involving only the two e g -like bands occupied by a single electron was considered (corresponding to the nominal d 7 occupancy of the Ni d-shell). It was concluded there that correlation effects may lead to a considerable enhancement of the OP, mostly due to the effect of the on-site Coulomb repulsion U , as emphasized in previous model studies.…”

Towards ab initio Calculations with the Dynamical Vertex Approximation

“…Already the first DFT+DMFT calculations allowed for a better understanding of the Mott-Hubbard transition in V 2 O 3 , 22) of δ-Pu, 23) the Ce volume collapse, 22) and magnetism in Fe and Ni. 24) More recently, among others, iron pnictides and their fluctuating magnetic moment, [25][26][27] complex oxide heterostructures, [28][29][30][31][32] nanoscopic structures, 33,34) thermoelectricity, [35][36][37] spin-orbit interactions, 38,39) and electronic entanglement 40) have been addressed.…”