Reiter's Polaron Wave Function Applied to a t<sub>2g</sub>Orbital t-J Model

Wohlfeld, Krzysztof; Oleś, Andrzej M.; Daghofer, Maria; Horsch, Peter

doi:10.12693/aphyspola.115.110

Cited by 2 publications

(1 citation statement)

References 7 publications

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“…Indeed, the coupling to orbitons increases the effective mass of a moving hole in e g systems [57]. The orbital part of the superexchange is classical t 2g systems, but also there weak quasiparticle dispersion arises from three-site processes [59] (see also this volume [60]).…”

Section: Summary and Open Problemsmentioning

confidence: 97%

Spin-Orbital Physics in Transition Metal Oxides

Oleś

2009

Acta Phys. Pol. A

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We present the main features of the spin-orbital superexchange which describes the magnetic and optical properties of the Mott insulators with orbital degrees of freedom. In contrast to the SU(2) symmetry of spin superexchange, the orbital part of the superexchange obeys the lower cubic symmetry of the lattice and is intrinsically frustrated. This intrinsic frustration and spin-orbital entanglement induce enhanced quantum fluctuations, and we point out a few situations where this leads to disordered states. Strong coupling between the spin and orbital degrees of freedom is discussed on the example of the RVO 3 perovskites, with R standing for rare-earth ion, La,. . .,Lu. We explain the observed evolution of the orbital T OO and Néel T N1 transition temperature in the RVO 3 series with decreasing ionic radius r R . A few open problems and the current directions of research in the field of spin-orbital physics are pointed out. Orbital versus spin superexchangeIn recent years the physical properties of Mott (or charge transfer) insulators are in the focus of interest in the condensed matter theory [1]. In order to develop theoretical understanding of complex phenomena in doped correlated insulators, including high temperature superconductivity in the cuprates and the colossal magnetoresistance (CMR) in the manganites, it is necessary to describe first the undoped materials, such as La 2 CuO 4 and LaMnO 3 . In both cases the local Coulomb interactions (Hubbard U ) is large and suppresses charge fluctuations, leading to low-energy effective Hamiltonians with superexchange interactions which stabilize antiferromagnetic (AF) spin order at low temperature [2,3]. However, these two compounds are qualitatively quite different. On the one hand, the degeneracy of partly filled e g orbitals is lifted in La 2 CuO 4 by the tetragonal distortions of CuO 6 octahedra, resulting in two-dimensional (2D) AF superexchange of S = 1/2 holes in x 2 − y 2 orbitals of Cu 2+ ions. On the other hand, in LaMnO 3 e g orbital degeneracy plays a fundamental role and, together with the Jahn-Teller (JT) distortions, is required to understand the origin of the anisotropic A-type AF (A-AF) order [4]. As realized already three decades ago [2], in this latter case the orbital degrees of freedom, which are described by the components |x ≡(1) of pseudospin τ = 1/2 and contribute explicitly to the structure of the superexchange. Thus they have to be included on equal footing with ionic spins in a spinorbital superexchange model. In the last two decades several new concepts were developed, such as enhanced quantum fluctuations due to orbital degrees of freedom which participate in joint spin-orbital excitations [5], and spin-orbital entanglement which occurs in cases when spin and orbital operators cannot be decoupled from each other [6]. The actual physical problems in this emerging and rapidly developing field were reviewed in the Focus Issue Orbital Physics in New Journal of Physics [7] a few years ago. Here we want to focus on a few representative r...

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Section: Summary and Open Problemsmentioning

confidence: 97%

Spin-Orbital Physics in Transition Metal Oxides

Oleś

2009

Acta Phys. Pol. A

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Quantum phase transitions in exactly solvable one-dimensional compass models

2014

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We present an exact solution for a class of one-dimensional compass models which stand for interacting orbital degrees of freedom in a Mott insulator. By employing the Jordan-Wigner transformation we map these models on noninteracting fermions and discuss how spin correlations, high degeneracy of the ground state, and Z2 symmetry in the quantum compass model are visible in the fermionic language. Considering a zigzag chain of ions with singly occupied eg orbitals (eg orbital model) we demonstrate that the orbital excitations change qualitatively with increasing transverse field, and that the excitation gap closes at the quantum phase transition to a polarized state. This phase transition disappears in the quantum compass model with maximally frustrated orbital interactions which resembles the Kitaev model. Here we find that finite transverse field destabilizes the orbital-liquid ground state with macroscopic degeneracy, and leads to peculiar behavior of the specific heat and orbital susceptibility at finite temperature. We show that the entropy and the cooling rate at finite temperature exhibit quite different behavior near the critical point for these two models.

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Reiter's Polaron Wave Function Applied to a t_2gOrbital t-J Model

Cited by 2 publications

References 7 publications

Spin-Orbital Physics in Transition Metal Oxides

Spin-Orbital Physics in Transition Metal Oxides

Quantum phase transitions in exactly solvable one-dimensional compass models

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Reiter's Polaron Wave Function Applied to a t2gOrbital t-J Model

Cited by 2 publications

References 7 publications

Spin-Orbital Physics in Transition Metal Oxides

Spin-Orbital Physics in Transition Metal Oxides

Quantum phase transitions in exactly solvable one-dimensional compass models

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Reiter's Polaron Wave Function Applied to a t_2gOrbital t-J Model