Spin and orbital occupation and phase transitions in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">V</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Park, J.-H.; Tjeng, L. H.; Tanaka, A.; Allen, J. W.; Chen, C. T.; Metcalf, P.; Honig, J. M.; Groot, Frank M. F. de; Sawatzky, G. A.

doi:10.1103/physrevb.61.11506

Cited by 215 publications

(219 citation statements)

References 44 publications

Supporting

Mentioning

184

Contrasting

Unclassified

Order By: Relevance

“…Indeed, the short range magnetic fluctuations observed by neutron scattering experiments 6 in the paramagnetic phases imply a statistical occupancy of the two orbitally degenerate molecular states of Eq. (5.5) and xray absorption spectra 14 show evidence of an average 25% occupancy of the a 1g and 75% of e g orbitals. This is very near to the totally symmetric occupation of the three orbitals (1/3 each), restoring in such a way the cubic symmetry.…”

Section: B Trigonal Distortionmentioning

confidence: 99%

“…This finding was pointing to an inconsistency of the interpretative framework. Additional evidence for a spin S = 1 state of the Vanadium atoms came from the interpretation of linear dichroism in the Vanadium L-edge absorption spectra, 14 where evidence of a reduced occupation of a 1g orbitals was also found (25% in the PM phase, 20% in the PI phase, 17% in the AFI phase, instead of the 50% postulated by CNR). These are strong indication that in the AFI phase of V 2 O 3 intra-atomic correlations prevail over band delocalization, contrary to the assumption made by CNR.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Spin-1 effective Hamiltonian with three degenerate orbitals: An application to the case of V2O3

2002

View full text Add to dashboard Cite

Motivated by recent neutron and x-ray observations in V2O3, we derive the effective Hamiltonian in the strong coupling limit of an Hubbard model with three degenerate t2g states containing two electrons coupled to spin S = 1, and use it to re-examine the low-temperature ground-state properties of this compound. An axial trigonal distortion of the cubic states is also taken into account. Since there are no assumptions about the symmetry properties of the hopping integrals involved, the resulting spin-orbital Hamiltonian can be generally applied to any crystallographic configuration of the transition metal ion giving rise to degenerate t2g orbitals.Specializing to the case of V2O3 we consider the low temperature antiferromagnetic insulating phase. We find two variational regimes, depending on the relative size of the correlation energy of the vertical pairs and the in-plane interaction energy. The former favors the formation of stable molecules throughout the crystal, while the latter tends to break this correlated state. Using the appropriate variational wave functions we determine in both cases the minimizing orbital solutions for various spin configurations, compare their energies and draw the corresponding phase diagrams in the space of the relevant parameters of the problem. We find that none of the symmetry-breaking stable phases with the real spin structure presents an orbital ordering compatible with the magnetic space group indicated by very recent observations of non-reciprocal x-ray gyrotropy in V2O3. We do however find a compatible solution with very small excitation energy in two distinct regions of the phase space, which might turn into the true ground state of V2O3 due to the favorable coupling with the lattice. We illustrate merits and drawbacks of the various solutions and discuss them in relation to the present experimental evidence.

show abstract

Section: B Trigonal Distortionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Spin-1 effective Hamiltonian with three degenerate orbitals: An application to the case of V2O3

2002

View full text Add to dashboard Cite

show abstract

“…Recent polarized X-ray scattering results of Park et al [5] require, however, an interpretation in terms of a spin S = 1 at each V site, with a mixed orbital e π g a 1g : e π g e π g = x : (1 − x) configuration. An exciting conclusion from these results is that the above ratio changes its value abruptly at the MIT, forcing one to abandon the one-band Hubbard model to describe V 2 O 3 .…”

mentioning

confidence: 99%

Orbital Switching and the First-Order Insulator-Metal Transition in ParamagneticV2O3

2003

View full text Add to dashboard Cite

The first-order metal-insulator transition (MIT) in paramagnetic V2O3 is studied within the ab-initio scheme LDA+DMFT, which merges the local density approximation (LDA) with dynamical mean field theory (DMFT). With a fixed value of the Coulomb U = 6.0 eV , we show how the abrupt pressure driven MIT is understood in a new picture: pressure-induced decrease of the trigonal distortion within the strong correlation scenario (which is not obtained within LDA). We find good quantitative agreement with (i) switch of the orbital occupation of (a1g, e π g1 , e π g2 ) and the spin state S = 1 across the MIT, (ii) thermodynamics and dc resistivity, and (iii) the one-electron spectral function, within this new scenario.PACS numbers: 71.28+d,71.30+h,72.10-dThe spectacular metal-insulator transition (MIT) in the paramagnetic (P) state in V 2 O 3 has long been considered as a classic, and by now almost a textbook version of correlation-driven MIT in a one-band correlated system described by the one-band Hubbard model [1]. This conventional wisdom has been recently challenged by new experiments, clearly showing the coupled spinorbital character of the system, and necessitating a revision in terms of a multiband picture.The conventionally accepted picture rested upon the following argument. In the high-T phase, V 2 O 3 exists in the corundum structure, and with a 3d 2 state (V 3+ ), the two e σ g orbitals are empty, while the triply degenerate t 2g orbitals are filled by two electrons. This triple degeneracy is lifted by a small trigonal distortion, leading to a singly occupied a 1g orbital oriented along the c-axis, and doubly degenerate planar e π g orbitals, occupied by the second electron. Castellani et al. [2] proposed that strong covalent effects lead to a bonding singlet a 1g state involving two V ions along the c-axis. The remaining electron in the two-fold degenerate e π g orbitals gives rise to a S = 1/2 model with orbital degeneracy. This inspired development of theoretical techniques, culminating in the dynamical mean field theory (DMFT) [3], leading to considerable improvement in our understanding of the MIT. Within the basic picture [2], Rozenberg et al.[4] used DMFT for one-and two-orbital Hubbard models with Bethe density-of-states to study the MIT in V 2 O 3 .Recent polarized X-ray scattering results of Park et al.[5] require, however, an interpretation in terms of a spin S = 1 at each V site, with a mixed orbital e π g a 1g : e π g e π g = x : (1 − x) configuration. An exciting conclusion from these results is that the above ratio changes its value abruptly at the MIT, forcing one to abandon the one-band Hubbard model to describe V 2 O 3 . Notice that this implies an important role for the trigonal splitting, since the lower-lying orbital will be more "localized" when local Coulomb interactions are switched on. This raises questions concerning a possible link between the orbital "switching" and the drastic change in the electronic state, and to a possible common underlying origin.The high-spin ground state res...

show abstract

“…This has recently been criticized for not respecting the strong on-site coulomb repulsion and Hund's rule coupling 9,10 . This criticism is supported by polarized soft x-ray experiments 9 , and strongly suggests that the effective spin on a V ion should have S = 1 instead of S = 1/2. Recently, a S = 1 model incorporating the orbital degree of freedom has been introduced 11 .…”

mentioning

confidence: 99%

Theory for Phase Transitions in InsulatingV2O3

Joshi

Zhang

2001

Phys. Rev. Lett.

View full text Add to dashboard Cite

We show that the recently proposed S = 2 bond model with orbital degrees of freedom for insulating V2O3 not only explains the anomalous magnetic ordering, but also other mysteries of the magnetic phase transition. The model contains an additional orbital degree of freedom that exhibits a zero temperature quantum phase transition in the Ising universality class.PACS numbers: 71.30.+h, 75.50.Ee The metal-insulator transition in vanadium oxide (V 2 O 3 ) has long been hailed as a physical realization of the Mott transition 1-3 . However, the insulating phase displays essential deviations from the standard Mott insulator with only spin degrees of freedom. For example, while it undergoes a transition from paramagnetic to antiferromagnetic (AF) insulator with decreasing temperature, the magnetic ordering pattern observed 4-6 (hitherto called RS) is not that of the simplest two-sublattice Neel state (hitherto referred to as AS). Some time ago, Castellani, Natoli, and Ranninger (CNR) 7 proposed a model in which the low energy degrees of freedom for each V ion are a spin (S = 1/2) coupled to doubly degenerate orbital. They showed that within certain parameter regime, the ground state exhibits the RS magnetic ordering pattern together with orbital ordering. Recently, resonant x-ray scattering experiments 8 have observed orbital ordering in V 2 O 3 with an ordering wavevector consistent with one of the ordered state (so-called RO state) obtained by CNR.The CNR model relies on one out of the two electrons on a V ion forming a spin singlet bond with its counterpart on the neighboring V ion along the c-axis, leaving one electron occupying doubly degenerate orbitals on each V ion. This has recently been criticized for not respecting the strong on-site coulomb repulsion and Hund's rule coupling 9,10 . This criticism is supported by polarized soft x-ray experiments 9 , and strongly suggests that the effective spin on a V ion should have S = 1 instead of S = 1/2. Recently, a S = 1 model incorporating the orbital degree of freedom has been introduced 11 . In this model V-V pair along c-axis is locked ferromagnetically into a total spin 2 "bond" with a double orbital degeneracy. These bonds occupy a lattice that is topologically equivalent to a cubic lattice (Fig. 1). Virtual in-plane hopping in the honeycomb planes couple such bonds to their neighbors. For Hund's rule coupling and hopping constants consistent with reported/expected values, it was shown that the ground state has RS magnetic and ferro-orbital (FO) order. The FO ordering was shown to be also consistent with the resonant x-ray experiments. In addition to the anomalous RS magnetic order, there are other mysteries associated with the V 2 O 3 insulator 12 : I) the magnetic and orbital ordering occur at the same transition temperature 8 , in contrast to the Jahn-Teller transitions observed in other transition metal oxides like MnO; II) the transition is strongly first order 13 ; and III) above the transition temperature, neutron scattering observes a relatively broad p...

show abstract

Spin and orbital occupation and phase transitions inV2O3

Cited by 215 publications

References 44 publications

Spin-1 effective Hamiltonian with three degenerate orbitals: An application to the case of V2O3

Spin-1 effective Hamiltonian with three degenerate orbitals: An application to the case of V2O3

Orbital Switching and the First-Order Insulator-Metal Transition in ParamagneticV2O3

Theory for Phase Transitions in InsulatingV2O3

Contact Info

Product

Resources

About