Noncollinear Magnetic Order Stabilized by Entangled Spin-Orbital Fluctuations

Brzezicki, Wojciech; Dziarmaga, Jacek; Oleś, Andrzej M.

doi:10.1103/physrevlett.109.237201

Cited by 43 publications

(97 citation statements)

References 69 publications

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“…This is not so surprising as one expects that isotropic spin-orbital interactions would lead instead to uniform phases only. In each case the effective exchange interaction changes sign in one (either spin or orbital) channel which resembles the mechanism of exotic magnetic order found in the Kugel-Khomskii model [85].…”

Section: B Isotropic Spin-orbital Su(2)⊗su(2) Modelmentioning

confidence: 99%

Quantum entanglement in the one-dimensional spin-orbitalSU(2)⊗XXZmodel

2015

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We investigate the phase diagram and the spin-orbital entanglement of a one-dimensional SU(2)⊗XXZ model with SU(2) spin exchange and anisotropic XXZ orbital exchange interactions and negative exchange coupling. As a unique feature, the spin-orbital entanglement entropy in the entangled ground states increases here linearly with system size. In the case of Ising orbital interactions we identify an emergent phase with long-range spin-singlet dimer correlations triggered by a quadrupling of correlations in the orbital sector. The peculiar translational invariant spin-singlet dimer phase has finite von Neumann entanglement entropy and survives when orbital quantum fluctuations are included. It even persists in the isotropic SU(2)⊗SU(2) limit. Surprisingly, for finite transverse orbital coupling the long-range spin singlet correlations also coexist in the antiferromagnetic spin and alternating orbital phase making this phase also unconventional. Moreover we also find a complementary orbital singlet phase that exists in the isotropic case but does not extend to the Ising limit. The nature of entanglement appears essentially different from that found in the frequently discussed model with positive coupling. Furthermore we investigate the collective spin and orbital wave excitations of the disentangled ferromagnetic-spin/ferro-orbital ground state and explore the continuum of spin-orbital excitations. Interestingly one finds among the latter excitations two modes of exciton bound states. Their spin-orbital correlations differ from the remaining continuum states and exhibit logarithmic scaling of the von Neumann entropy with increasing system size. We demonstrate that spin-orbital excitons can be experimentally explored using resonant inelastic x-ray scattering, where the strongly entangled exciton states can be easily distinguished from the spin-orbital continuum.

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Section: B Isotropic Spin-orbital Su(2)⊗su(2) Modelmentioning

confidence: 99%

Quantum entanglement in the one-dimensional spin-orbitalSU(2)⊗XXZmodel

2015

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“…Thereby we summarize the results of the earlier studies for a 2D monolayer [47], bilayer [48], and a 3D perovskite (cubic) system [49]. We show below that spin-orbital fluctuations and entanglement [7,15] plays a very important role here and stabilizes exotic types of magnetic order in all these systems.…”

Section: Introductionmentioning

confidence: 94%

“…In a bilayer two ab planes are connected by interlayer bonds along the c axis [48], while a monolayer has only bonds within a single ab plane [47], i.e., γ = a, b. In all these cases spin interactions are described with the help of spin projection operators on a triplet or a singlet configuration on a bond ij ,…”

Section: Kugel-khomskii Modelmentioning

confidence: 99%

“…In reality the angles for the AO states vary in a continuous way as functions of the CF parameter E z /J, and therefore an efficient way of solving the one-site MF equations consists of assuming possible magnetic orders and for each of them deriving the effective orbital-only model. Such models are next compared and the phases with the lowest energy is found, as presented below for the case of the 2D monolayer, [47], the KK bilayer [48], and for the 3D cubic model [49]. The simplest approximation to obtain the possible types of order in a spin-orbital model, like the KK models Eq.…”

Section: Mean-field Phase Diagramsmentioning

confidence: 99%

“…Phase diagrams of the KK models in the single-site MF approximation as obtained for: (a) the 2D monolayer [47], (b) the bilayer [48], and (c) the 3D perovskite system [49]. Shaded dark gray (green) areas indicate phases with AO order: FM and G-AF phase for the monolayer (a), and the A-AF, C-AF and G-AF phases for the bilayer (b) and the 3D perovskite (c) [here the FM phases which coexist also with the AO order are not shadded for clarity].…”

Section: B Single-site Mean-field Approximationmentioning

confidence: 99%

See 2 more Smart Citations

Exotic Spin Order due to Orbital Fluctuations

2014

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We investigate the phase diagrams of the spin-orbital d9 Kugel-Khomskii model for increasing system dimensionality: from the square lattice monolayer, via the bilayer to the cubic lattice. In each case we find strong competition between different types of spin and orbital order, with entangled spin-orbital phases at the crossover from antiferromagnetic to ferromagnetic correlations in the intermediate regime of Hund's exchange. These phases have various types of exotic spin order and are stabilized by effective interactions of longer range which follow from enhanced spin-orbital fluctuations. We find that orbital order is in general more robust and spin order melts first under increasing temperature, as observed in several experiments for spin-orbital systems.

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Novel Spin-Orbital Phases Induced by Orbital Dilution

Brzezicki

Cuoco

Oleś

2015

J Supercond Nov Magn

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We demonstrate that magnetic 3d impurities with S = 3/2 spins and no orbital degree of freedom induce changes of spin-orbital order in a 4d 4 Mott insulator with S = 1 spins. Impurities act either as spin defects which decouple from the surrounding ions, or trigger orbital polarons along 3d-4d bonds. The 4d-4d superexchange in the host J host competes with 3d-4d superexchange J imp -it depends on which orbital is doubly occupied. The spinorbital order within the host is totally modified at doping x = 1/4. Our findings provide new perspective for future theoretical and experimental studies of doped transitionmetal oxides. The well-known example are hole-doped La 1−x Sr x MnO 3 manganites with colossal magnetoresistance [3]. At low doping, orbital polarons emerge in an antiferromagnetic (AF) system by double-exchange mechanism [4], while at higher doping, spin order changes globally to a FM metal coexisting with an e g orbital liquid phase [5]. But a different scenario is also possible-frustrated spin-orbital interactions may lead in some cases to the collapse of any long range order and to a spin-orbital liquid suggested for LiNiO 2 [6]. However, spin and orbital energy scales are here quite different, and the reasons behind the absence of magnetic long range order are indeed more subtle and not yet fully understood [7]. KeywordsA rather unique example of a spin-orbital system are perovskite vanadates, where interesting competition between two types of spin-orbital order was observed [8]. The theoretical spin-orbital model describes an interplay between S = 1 spins and τ = 1/2 orbital doublet {yz, zx} active along the c axis [9], while xy orbitals are filled by one electron each. In addition, G-type AF (G-AF) order in YVO 3 is fragile and switches to C-type AF (C-AF) one in Y 1−x Ca x VO 3 [10], with staggered lines of one-dimensional (1D) FM order (Fig. 1), accompanied by G-type alternating orbital (G-AO) order. Already at low doping, x 0.02 finite spectral weight is generated within the Mott-Hubbard gap due to charge defects away from the VO 6 octahedra [11].

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Noncollinear Magnetic Order Stabilized by Entangled Spin-Orbital Fluctuations

Cited by 43 publications

References 69 publications

Quantum entanglement in the one-dimensional spin-orbitalSU(2)⊗XXZmodel

Quantum entanglement in the one-dimensional spin-orbitalSU(2)⊗XXZmodel

Exotic Spin Order due to Orbital Fluctuations

Novel Spin-Orbital Phases Induced by Orbital Dilution

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