Microscopic origin of diagonal stripe phases in doped nickelates

TL;DR

This study explores the microscopic mechanisms behind diagonal stripe phases in doped nickelates, emphasizing the importance of off-diagonal e_g hopping terms in stabilizing experimentally observed stripe structures.

Contribution

It compares two models to identify the role of off-diagonal hopping in stripe phase stability, revealing the significance of realistic hopping terms for nickelates.

Findings

Diagonal stripe phases with nearly one hole per atom are most stable in nickelates.

Off-diagonal e_g hopping terms are crucial for stripe formation in La_2-xSr_xNiO_4.

Differences between nickelates and cuprates are clarified through model comparisons.

Abstract

We investigate the electron density distribution and the stability of stripe phases in the realistic two-band model with hopping elements between e_g orbitals at Ni sites on the square lattice, and compare these results with those obtained for the doubly degenerate Hubbard model with two equivalent orbitals and diagonal hopping. For both models we determine the stability regions of filled and half-filled stripe phases for increasing hole doping x=2-n in the range of x<0.4, using Hartree-Fock approximation for large clusters. In the parameter range relevant to the nickelates, we obtain the most stable diagonal stripe structures with filling of nearly one hole per atom, as observed experimentally. In contrast, for the doubly degenerate Hubbard model the most stable stripes are somewhat reminiscent of the cuprates, with half-filled atoms at the domain wall sites. This difference elucidates the crucial role of the off-diagonal e_g hopping terms for the stripe formation in La_2-xSr_xNiO_4. The influence of crystal field is discussed as well.