Jahn-Teller mechanism of stripe formation in doped layered La$_{2-x}$Sr$_x$NiO$_4$ nickelates

TL;DR

This paper presents an effective model for layered nickelates that incorporates Jahn-Teller distortions, successfully reproducing experimental charge, spin, and orbital orderings, and highlighting the crucial role of Jahn-Teller effects in stripe formation.

Contribution

The study introduces a new effective Hamiltonian including Jahn-Teller coupling, explaining stripe and checkerboard phases in doped La$_{2-x}$Sr$_x$NiO$_4$ nickelates.

Findings

Jahn-Teller distortions are key to stabilizing observed phases.

The model reproduces charge, spin, and orbital order at specific dopings.

Weak Jahn-Teller effects still have a significant impact on phase stability.

Abstract

We introduce an effective model for $e_g$ electrons to describe quasi-two-dimensional layered La$_{2-x}$Sr$_{x}$NiO$_4$ nickelates and study it using correlated wave functions on $8 \times 8 $ and $6 \times 6 $ clusters. The effective Hamiltonian includes the kinetic energy, on-site Coulomb interactions for $e_g$ electrons (intraorbital $U$ and Hund's exchange $J_H$) and the coupling between $e_g$ electrons and Jahn-Teller distortions (static modes). The experimental ground state phases with inhomogeneous charge, spin and orbital order at the dopings $x=1/3$ and $x=1/2$ are reproduced very well by the model. Although the Jahn-Teller distortions are weak, we show that they play a crucial role and stabilize the observed cooperative charge, magnetic and orbital order in form of a diagonal stripe phase at $x=1/3$ doping and a checkerboard phase at $x=1/2$ doping.