Jahn-Teller mechanism of stripe formation in doped layered La 2 - XSrxNiO4 nickelates

Marian Smoluchowski Institute of Physics, Jagellonian University, Reymonta 4, PL-30059 Kraków, Poland.
Journal of Physics Condensed Matter (Impact Factor: 2.35). 06/2011; 23(26):265601. DOI: 10.1088/0953-8984/23/26/265601
Source: arXiv


We introduce an effective model for eg electrons to describe quasi-two-dimensional layered La2 − xSrxNiO4 nickelates and study it using correlated wavefunctions on 8 × 8 and 6 × 6 clusters. The effective Hamiltonian includes the kinetic energy, on-site Coulomb interactions for eg electrons (intraorbital U and Hund's exchange JH) and the coupling between eg 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 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 the form of a diagonal stripe phase at x = 1/3 doping and a chequerboard phase at x = 1/2 doping.

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    ABSTRACT: We review briefly several approaches used to investigate the stability of stripe phases in high temperature superconductors, where charge inhomogeneities arise from competing kinetic and magnetic energies. The mechanism of stripe formation, their consequences for the normal state and enhancement of pairing interaction triggered by charge inhomogeneities are briefly summarized. Finally, we demonstrate that orbital degeneracy ($i$) leads to a more subtle mechanism of stripe formation, and ($ii$) plays an important role and determines the symmetry of the superconducting state in pnictides.