Optical conductivity in the vicinity of a quantum critical point

Bogdanski, P.; Halaoui, Mohammed; Oleś, Andrzej M.; Frésard, Raymond

doi:10.1103/physrevb.82.195125

Cited by 5 publications

(3 citation statements)

References 62 publications

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“…In this latter situation the ground state is more classical and is not entangled as it follows from interactions induced by the lattice and not from the spin-orbital superexchange. Also in the regime of large Hund's exchange J H , ground states with coexisting FM and FO order may appear [117], similar to the FM/FO states in the SU(2) ⊗ SU(2) model. They contradict again the Goodenough-Kanamori rules, but are in fact disentangled-here quantum fluctuations are absent and play no role for their stability.…”

Section: Discussion and Summarymentioning

confidence: 84%

Fingerprints of spin–orbital entanglement in transition metal oxides

Oleś¹

2012

J. Phys.: Condens. Matter

124

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The concept of spin-orbital entanglement on superexchange bonds in transition metal oxides is introduced and explained on several examples. It is shown that spin-orbital entanglement in superexchange models destabilizes the long-range (spin and orbital) order and may lead either to a disordered spin-liquid state or to novel phases at low temperature which arise from strongly frustrated interactions. Such novel ground states cannot be described within the conventionally used mean field theory which separates spin and orbital degrees of freedom. Even in cases where the ground states are disentangled, spin-orbital entanglement occurs in excited states and may become crucial for a correct description of physical properties at finite temperature. As an important example of this behaviour we present spin-orbital entanglement in the RV O(3) perovskites, with R = La,Pr,…,Y b,Lu, where the finite temperature properties of these compounds can be understood only using entangled states: (i) the thermal evolution of the optical spectral weights, (ii) the dependence of the transition temperatures for the onset of orbital and magnetic order on the ionic radius in the phase diagram of the RV O(3) perovskites, and (iii) the dimerization observed in the magnon spectra for the C-type antiferromagnetic phase of Y V O(3). Finally, it is shown that joint spin-orbital excitations in an ordered phase with coexisting antiferromagnetic and alternating orbital order introduce topological constraints for the hole propagation and will thus radically modify the transport properties in doped Mott insulators where hole motion implies simultaneous spin and orbital excitations.

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Section: Discussion and Summarymentioning

confidence: 84%

Fingerprints of spin–orbital entanglement in transition metal oxides

Oleś¹

2012

J. Phys.: Condens. Matter

124

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“…Summarizing, the SOE in the excited states is visible in the magnetic and optical properties of the vanadium perovskites, and any theoretical treatment has to go beyond a simple picture established by the Goodeough-Kanamori rules, and one has to go beyond this paradigm also in alkali RO 2 hyperoxides (with R=K,Rb,Cs) [43] or in finite clusters [44]. In the case of quantum states, these rules have to be generalized as follows: In the wave functions a component with spin-singlet and orbital-triplet coexists with a component with spin-triplet and orbital-singlet.…”

Section: Entanglement In Spin-orbital Modelsmentioning

confidence: 99%

Frustration and Entanglement in Compass and Spin-Orbital Models

Oleś

2015

Acta Phys. Pol. A

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We review the consequences of intrinsic frustration of the orbital superexchange and of spinorbital entanglement. While Heisenberg perturbing interactions remove frustration in the compass model, the lowest columnar excitations are robust in the nanoscopic compass clusters and might be used for quantum computations. Entangled spin-orbital states determine the ground states in some cases, while in others concern excited states and lead to measurable consequences, as in the RVO3 perovskites. On-site entanglement for strong spin-orbit coupling generates the frustrated Kitaev-Heisenberg model with a rich magnetic phase diagram on the honeycomb lattice. Frustration is here reflected in hole propagation which changes from coherent in an antiferromagnet via hidden quasiparticles in zigzag and stripe phases to entirely incoherent one in the Kitaev spin liquid. PACS numbers: 75.10.Jm, 03.67.-a, 75.25.Dk, 79.60.-i Frustration in Compass ModelsAlthough the 2D Ising and compass model are in the same universality class, they are quite different -the

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“…In that case spin-orbital models provide a framework to analyze a wealth of properties (for a recent reference see Oleś et al [1] and references therein). Nevertheless, many systems are rather tracked down to be in the intermediate coupling regime, where, for example, phase transitions between ferromagnetic and antiferromagnetic phases can take place (see, e. g., [2]). Such situations are not covered by the standard spin-orbital models, and higher orders in the expansion in t are needed.…”

Section: Introductionmentioning

confidence: 99%

Magnetic transitions in strong coupling expansions for nearly degenerate states

2012

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A strong coupling expansion for a two-band Hubbard model on two sites with nearly degenerate states is considered. A comparative analysis is performed for different schemes of perturbation theory which are applicable to systems with nearly degenerate states. A fourth order approach which builds on a four-dimensional low-energy subspace with nearly degenerate states captures accurately the transition from an antiferromagnetic to a ferromagnetic ground state at large on-site Coulomb interaction.

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Optical conductivity in the vicinity of a quantum critical point

Cited by 5 publications

References 62 publications

Fingerprints of spin–orbital entanglement in transition metal oxides

Fingerprints of spin–orbital entanglement in transition metal oxides

Frustration and Entanglement in Compass and Spin-Orbital Models

Magnetic transitions in strong coupling expansions for nearly degenerate states

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