Mott Transition and Suppression of Orbital Fluctuations in Orthorhombic 3 d 1 Perovskites

University of Pavia, Ticinum, Lombardy, Italy
Physical Review Letters (Impact Factor: 7.51). 05/2004; 92(17):176403. DOI: 10.1103/PhysRevLett.92.176403
Source: PubMed


Using ${t}_{2g}$ Wannier functions, a low-energy Hamiltonian is derived for orthorhombic $3{d}^{1}$ transition-metal oxides. Electronic correlations are treated with a new implementation of dynamical mean-field theory for noncubic systems. Good agreement with photoemission data is obtained. The interplay of correlation effects and cation covalency (${\mathrm{GdFeO}}_{3}$-type distortions) is found to suppress orbital fluctuations in ${\mathrm{LaTiO}}_{3}$ and even more in ${\mathrm{YTiO}}_{3}$, and to favor the transition to the insulating state.

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Available from: Eva Pavarini, Sep 30, 2015
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    • "4d 1 systems usually have a reduced SOC and some enhanced correlation strengths. In 3d systems, a much stronger correlation strength leads to a Mott transition, which has been intensively discussed,[8] while SOC is usually minor. Here, we focus on the recently synthesized BaFe 2 (PO 4 ) 2 compound with a honeycomb lattice of high spin d 6 Fe 2+ ions, leading to an effectively isolated minority-spin d 1 configuration due to a large exchange splitting of the high spin Fe ion. "
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    ABSTRACT: BaFe2(PO4)2 is an unusual Ising insulating ferromagnet based on the Fe$^{2+}$ spin S=2 ion, whose susceptibility suggests in addition a large orbital component to the Fe local moment. We apply density functional theory based methods to obtain a microscopic picture of the competing interactions and the critical role of spin-orbit coupling (SOC) in this honeycomb lattice system. The low T ferromagnetic phase displays a half-semimetallic Dirac point pinning the Fermi level and preventing gap opening before consideration of SOC, presenting a case in which correlation effects modeled by a repulsive Hubbard $U$ fails to open a gap. Simultaneous inclusion of both correlation and SOC drives a large orbital moment M_L of more than 0.7 $\mu_B$ (essentially L=1) for spin aligned along the c-axis, with a gap comparable with the inferred experimental value. The large orbital moment accounts for the large Ising anisotropy, in spite of the small magnitude of the SOC strength on the 3d (Fe) ion. Ultimately, the Mott-Hubbard gap is enabled by degeneracy lifting by SOC and the large Fe moments, rather than by standard Hubbard interactions alone. We suggest that competing orbital occupations are responsible for the structural transitions involved in the observed re-entrant rhombohedral-triclinic-rhombohedral sequence.
    Physical Review B 06/2015; 92(12). DOI:10.1103/PhysRevB.92.125109 · 3.74 Impact Factor
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    ABSTRACT: We review recent results on the properties of materials with correlated electrons obtained within the LDA+DMFT approach, a combination of a conventional band structure approach based on the local density approximation (LDA) and the dynamical mean-field theory (DMFT). The application to four outstanding problems in this field is discussed: (i) we compute the full valence band structure of the charge-transfer insulator NiO by explicitly including the p-d hybridization, (ii) we explain the origin for the simultaneously occuring metal-insulator transition and collapse of the magnetic moment in MnO and Fe2O3, (iii) we describe a novel GGA+DMFT scheme in terms of plane-wave pseudopotentials which allows us to compute the orbital order and cooperative Jahn-Teller distortion in KCuF3 and LaMnO3, and (iv) we provide a general explanation for the appearance of kinks in the effective dispersion of correlated electrons in systems with a pronounced three-peak spectral function without having to resort to the coupling of electrons to bosonic excitations. These results provide a considerable progress in the fully microscopic investigations of correlated electron materials.
    The European Physical Journal Special Topics 12/2010; 180(1):5-28. DOI:10.1140/epjst/e2010-01209-0 · 1.40 Impact Factor
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    ABSTRACT: databases like Chemical Abstracts (CAS) or Physics Abstracts (INSPEC) are conducted be- side the SCI, only a few conference proceedings
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