Orbital polaron in double-exchange ferromagnets

Berg, T. L. van den; Lombardo, P.; Kuzian, R. O.; Hayn, R.

doi:10.1103/physrevb.86.235114

Cited by 1 publication

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References 32 publications

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“…4 This latter compound undergoes a transition from the GC phase to the CG phase 36 at rather low doping x ∼ 0.02 within the insulating phase. It was pointed out 23 that the double exchange [37][38][39][40] is the mechanism responsible for this transition in antiferromagnetic (AF) phases, similar to the transition from the G-type AF (G-AF) to C-type AF (C-AF) order in electron doped manganites. 41 In addition, the change of superexchange interaction in the vicinity of the holes 42 bound to the defects has a strong influence on the relative energy of these states.…”

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confidence: 94%

Defect states and excitations in a Mott insulator with orbital degrees of freedom: Mott-Hubbard gap versus optical and transport gaps in doped systems

2013

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We address the role played by charged defects in doped Mott insulators with active orbital degrees of freedom. It is observed that defects feature a rather complex and rich physics, which is well captured by a degenerate Hubbard model extended by terms that describe crystal-field splittings and orbital-lattice coupling, as well as by terms generated by defects such as the Coulomb potential terms that act both on doped holes and on electrons within occupied orbitals at undoped sites. We show that the multiplet structure of the excited states generated in such systems by strong electron interactions is well described within the unrestricted Hartree-Fock approximation, once the symmetry breaking caused by the onset of magnetic and orbital order is taken into account. Furthermore, we uncover spectral features that arise within the Mott-Hubbard gap and in the multiplet spectrum at high energies due to the presence of defect states and strong correlations. These features reflect the action on electrons/holes of the generalized defect potential that affects charge and orbital degrees of freedom, and indirectly also spin ones. This study elucidates the mechanism behind the Coulomb gap appearing in the band of defect states and investigates the dependence on the electron-electron interactions and the screening by the orbital-polarization field. As an illustrative example of our general approach, we present explicit calculations for the model describing three t2g orbital flavors in the perovskite vanadates doped by divalent Sr or Ca ions, such as in La1−xSrxVO3 and Y1−xCaxVO3 systems. We analyze the orbital densities at vanadium ions in the vicinity of defects and the excited defect states which determine the optical and transport gaps in doped systems

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