Exotic Spin Order due to Orbital Fluctuations

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

doi:10.12693/aphyspola.126.a-40

Cited by 4 publications

(2 citation statements)

References 58 publications

(106 reference statements)

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“…Nevertheless it revealed peculiar types of spin ordering, namely noncollinear magnetic patterns depicted in figures 5(c) and (d). The mech anism that can stabilize such ordering in absence of SOC are entangled spinorbital fluctuations on lattice bonds, also dis cussed in [111][112][113]. Noncollinear phases were observed in spinorbital phase diagrams, obtained via cluster meanfield method (Bethe-Peierls-Weiss method, also used in analogical bilayer case [28]), shown in figures 5(a) and (b).…”

Section: Noncollinear Magnetic Order Stabilized By Orbital Fluctuationsmentioning

confidence: 91%

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Spin, orbital and topological order in models of strongly correlated electrons

Brzezicki

2019

J. Phys.: Condens. Matter

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Different types of order are discussed in the context of strongly correlated transition metal oxides, involving pure compounds and 3d 3 − 4d 4 and 3d 2 − 4d 4 hybrids. Apart from standard, longrange spin and orbital orders we observe also exotic non-colinear spin patterns. Such patters can arise in presence of atomic spinorbit coupling, which is a typical case, or due to spin-orbital entanglement at the bonds in its absence, being much less trivial.Within a special interacting onedimensional spin-orbital model it is also possible to find a rigorous topological magnetic order in a gapless phase that goes beyond any classification tables of topological states of matter. This is an exotic example of a strongly correlated topological state. Finally, in the less correlated limit of 4d 4 oxides, when orbital selective Mott localization can occur it is possible to stabilize by a 3d 3 doping one-dimensional zigzag antiferromagnetic phases. Such phases have exhibit nonsymmorphic spatial symmetries that can lead to various topological phenomena, like single and mutliple Dirac points that can turn into nodal rings or multiple topological charges protecting single Dirac points. Finally, by creating a onedimensional 3d 2 − 4d 4 hybrid system that involves orbital pairing terms, it is possible to obtain an insulating spin-orbital model where the orbital part after fermionization maps to a non-uniform Kitaev model. Such model is proved to have topological phases in a wide parameter range even in the case of completely disordered 3d 2 impurities. What more, it exhibits hidden Lorentz-like symmetries of the topological phase, that live in the parameters space of the model.

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Section: Noncollinear Magnetic Order Stabilized By Orbital Fluctuationsmentioning

confidence: 91%

“…The mechanism that can stabilize such ordering in absence of SOC are entangled spin-orbital fluctuations on lattice bonds, also dicussed in Refs. [105][106][107].…”

Section: Noncollinear Magnetic Order Stabilized By Orbital Fluctuationsmentioning

confidence: 99%

Spin, orbital and topological order in models of strongly correlated electrons

Brzezicki

2019

J. Phys.: Condens. Matter

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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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Spin-orbital order in the undoped manganite LaMnO3 at finite temperature

Snamina

Oleś

2016

Phys. Rev. B

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We investigate the evolution of spin and orbital order in undoped LaMnO3 under increasing temperature with a model including both superexchange and Jahn-Teller interactions. We used several cluster mean field calculation schemes and find coexisting A-type antiferromagnetic (A-AF) and C-type alternating orbital order at low temperature. The value of the Jahn-Teller coupling between strongly correlated eg orbitals is estimated from the orbital transition temperature at TOO 780 K. By a careful analysis of on-site and on-bond correlations we demonstrate that spinorbital entanglement is rather weak. We have verified that the magnetic transition temperature is influenced by entangled spin-orbital operators as well as by entangled orbital operators on the bonds but the errors introduced by decoupling such operators partly compensate each other. Altogether, these results justify why the commonly used disentangled spin-orbital model is so successful in describing the magnetic properties and the temperature dependence of the optical spectral weights for LaMnO3. Published in: Physical Review B 94, 214426 (2016).

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Exotic Spin Order due to Orbital Fluctuations

Cited by 4 publications

References 58 publications

Spin, orbital and topological order in models of strongly correlated electrons

Spin, orbital and topological order in models of strongly correlated electrons

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

Spin-orbital order in the undoped manganite LaMnO3 at finite temperature

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