Jahn–Teller mechanism of stripe formation in doped layered La2 − xSrxNiO4 nickelates

Marian Smoluchowski Institute of Physics, Jagellonian University, Reymonta 4, PL-30059 Kraków, Poland.
Journal of Physics Condensed Matter (Impact Factor: 2.36). 06/2011; 23(26):265601. DOI:10.1088/0953-8984/23/26/265601
Source: arXiv

ABSTRACT 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: In recent studies of La{sub 2-{ital x}}Sr{sub {ital x}}NiOâ it has been suggested that ordering of the dopant-induced holes occurs only commensurately at special values of {ital x}, such as 1/3 and 1/2. Commensurate order of both charge and spin densities has also been found in a crystal with {ital x}=0.20. The present neutron scattering study of an {ital x}=0.225 crystal demonstrates that the spin and charge order can also be incommensurate. In fact, the incommensurability is temperature dependent, as observed previously in LaâNiO{sub 4.125}, indicating that such behavior is intrinsic to the doped NiOâ layers and not dependent on ordering of the dopant ions. A careful analysis of the unusual variation of peak widths as a function of momentum transfer perpendicular to the planes shows that the charge- and spin-density modulations are tied to the lattice, with the shift in phase of the charge modulations from one layer to the next equal to exactly one in-plane lattice spacing. A comparison of results for a number of samples shows that the charge and spin ordering temperatures vary linearly with hole concentration, with charge order always occurring at higher temperature, clearly indicating that the ordering is driven by the charge. {copyright} {ital 1996 The American Physical Society.}
    Physical review. B, Condensed matter 01/1996; 54(17):12318-12323.
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    ABSTRACT: In doped Mott-Hubbard insulators, the electron-phonon interaction and strong Coulomb repulsion can reinforce each other to stabilize small polarons, domain walls, and charge-density waves. We discuss how the electron-phonon coupling stabilizes domain-wall states in an antiferromagnetic spin background for small doping, and promotes coupled spin- and charge-density wave transitions at larger doping, and we explain why this coupling is more important in the nickelate than in the cuprate. We discuss our results in the light of recent experiments on La2-xSrxNiO4+y.
    Physical review. B, Condensed matter 10/1994; 50(10):7222-7225.

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