Two dimensional model for correlated e_g electrons in doped nickelates

Abstract

We investigate the magnetic, orbital and charge instabilities in e g band for the average filling by 2 n x = -electrons per site, as in La 2-x Sr x NiO 4 . The calculations were performed on 8 × 8 clusters, with electron correlations included within the local ansatz method. The C-type antiferromagnetic phase was found in a broad range of doping, but distinct stripe phases could not be identified. The nonuniform orbital order is present for some dopings and couples to charge and spin order.

Interplay between the orbital and magnetic order in monolayer La1−xSr1+xMnO4manganites

“…The simplified crystal field term has to be included as one expects a finite anisotropy between two e g states in the geometry of a monolayer system. This model and/or the essential parts of it were studied earlier in numerous papers [1,3,6,12,13,22,23].…”

“…In contrast to equation (3), the sum over bonds i j includes each pair of nearest neighbour sites only once. Here the on-site Coulomb interaction element is denoted as U , Hund's exchange interaction is J H , and J stands for the superexchange interaction between frozen core t 2g electrons [3,15,[23][24][25]. The Hund's term, as given above in equation (5), is in fact a rather crude approximation.…”

“…In this way the correlation energy, E corr = E tot − E HF , is obtained. For technical details see [23,37]. For the correlation operators we use…”

Jahn–Teller distortions and the magnetic order in the perovskite manganites

“…In the next step each HF wave functions was independently modified to improve the energy and to include the electron correlations using the so-called local ansatz (for details see refs. [30][31][32][33]). We used the ansatz for the correlated ground state,…”

“…After completing the HF computations we performed correlation computations (as a second step for each investigated wavefunction) obtaining the total energy (9) and the correlation energy (10) (for more details see [30][31][32]). After obtaining the total energy for one configuration, we repeated the entire procedure from the beginning, i.e., we took another (second) set of HF initial conditions and repeated all computations to obtain the second candidate for the ground state.…”