Phase Diagram of Orbital-Selective Mott Transitions at Finite Temperatures

Inaba, Kazuaki; Koga, Akihisa; Suga, Sei–ichiro; Kawakami, Norio

doi:10.1143/jpsj.74.2393

Cited by 23 publications

(47 citation statements)

References 44 publications

(56 reference statements)

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“…At T ¼ 0:01 and 0.02, we find that in the curve of the specific heat coefficient, the broad peak appears around U$1:5, and another sharp one around U$5. This suggests that around U$1:5, the OSMT does not occur between the metallic and intermediate phases, but it is replaced by a crossover at the temperature [6]. On the other hand, the other Mott transition still occurs, where the jump singularity persists in both curves for g and S. In addition, the hysteresis is observed around there (not shown here), suggesting that the transition is of first-order at finite temperatures.…”

mentioning

confidence: 68%

Thermodynamic properties of the two-orbital Hubbard model

Koga

Suga

Kawakami

2007

Journal of Magnetism and Magnetic Materials

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confidence: 68%

Thermodynamic properties of the two-orbital Hubbard model

Koga

Suga

Kawakami

2007

Journal of Magnetism and Magnetic Materials

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“…11 Finally, the possibility of so-called orbital-selective Mott transitions in multiband systems has been discussed extensively in the literature. 7,[12][13][14][15][16] These different trends underline the remarkably rich physics of Mott transitions in multiorbital materials.…”

Section: Introductionmentioning

confidence: 97%

“…The latter picture would be analogous to the orbital-selective Mott transition, which can occur within single-site DMFT treatments of certain multiband systems. 7,[12][13][14][15][16] Another possibility, analogous to multiorbital materials such as LaTiO 3 , V 2 O 3 , and Ca 2 RuO 4 , is that a subset of cluster orbitals could exhibit a genuine Mott transition, while the remaining ones are pushed above or below the Fermi level at about the same critical U.…”

Section: Introductionmentioning

confidence: 99%

Multisite versus multiorbital Coulomb correlations studied within finite-temperature exact diagonalization dynamical mean-field theory

2008

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The influence of short-range Coulomb correlations on the Mott transition in the single-band Hubbard model at half filling is studied within cellular dynamical mean-field theory for square and triangular lattices. Finitetemperature exact diagonalization is used to investigate correlations within two-, three-, and four-site clusters. Transforming the nonlocal self-energy from a site basis to a molecular-orbital basis, we focus on the interorbital charge transfer between these cluster molecular orbitals in the vicinity of the Mott transition. In all cases studied, the charge transfer is found to be small, indicating weak Coulomb-induced orbital polarization despite sizable level splitting between orbitals. These results demonstrate that all cluster molecular orbitals take part in the Mott transition and that the insulating gap opens simultaneously across the entire Fermi surface. Thus, at half filling we do not find orbital-selective Mott transitions or a combination of band filling and Mott transition in different orbitals. Nevertheless, the approach toward the transition differs greatly between cluster orbitals, giving rise to a pronounced momentum variation along the Fermi surface, in agreement with previous works. The near absence of Coulomb-induced orbital polarization in these clusters differs qualitatively from single-site multiorbital studies of several transition-metal oxides, where the Mott phase exhibits nearly complete orbital polarization as a result of a correlation driven enhancement of the crystal-field splitting. The strong singleparticle coupling among cluster orbitals in the single-band case is identified as the source of this difference.

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“…This SFA, which is based on the LuttingerWard variational method, 96) allows us to deal with finite-temperature properties of the multi-orbital system efficiently, 20), 40) where standard DMFT with numerical methods may encounter some difficulties in practical calculations when the number of orbitals increases.…”

Section: Self-energy Functional Approachmentioning

confidence: 99%

“…The first-order critical point U c ∼ 2.33 for T = 0.002 is estimated by comparing the grand potential for each phase. 20) The phase diagram thus obtained by SFA is shown in Fig. 12.…”

Section: Phase Diagram At Finite Temperaturesmentioning

confidence: 99%

Mott Transitions in Two-Orbital Hubbard Systems

Koga¹,

Kawakami²

2005

Prog. Theor. Phys. Suppl.

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We investigate the Mott transitions in two-orbital Hubbard systems. Applying the dynamical mean field theory and the self-energy functional approach, we discuss the stability of itinerant quasi-particle states in each band. It is shown that separate Mott transitions occur at different Coulomb interaction strengths in general. On the other hand, if some special conditions are satisfied for the interactions, spin and orbital fluctuations are equally enhanced at low temperatures, resulting in a single Mott transition. The phase diagrams are obtained at zero and finite temperatures. We also address the effect of the hybridization between two orbitals, which induces the Kondo-like heavy fermion states in the intermediate orbital-selective Mott phase. §1. Introduction Strongly correlated electron systems with some orbitals have been investigated extensively. 1), 2) In particular, substantial progress in the theoretical understanding of the Mott transition in multiorbital systems has been made by dynamical meanfield theory (DMFT) 3)-7) calculations. 8)-40) Among them, the orbital-selective Mott transition (OSMT) 41) has been one of the most active topics in this context. A typical material is the single-layer isovalent ruthenate alloy Ca 2−x Sr x RuO 4 . 42)-44) The end-member Sr 2 RuO 4 is a well-known unconventional superconductor, 45), 46) while Ca 2 RuO 4 is a Mott-insulating S = 1 antiferromagnet. 47)-49) The relevant 4d-orbitals belong to the t 2g -subshell. The planar structure prevents the hybridization between orbitals which have even (d xy ) and odd parity (d yz , d zx ) under the reflection z → −z. The complex evolution between these different end-members has stimulated theoretical investigations, 50)-53) and among others to the proposal of the OSMT: some of the d-orbitals fall in localized states, while the others provide itinerant electrons. The OSMT scenario could explain the experimental observation of a localized spin S = 1/2 in the metallic system at x ∼ 0.5 in Ca 2−x Sr x RuO 4 , which is difficult to obtain from the entirely itinerant description. 41), 52), 54) Another example of the OSMT is the compound La n+1 Ni n O 3n+1 . 55) It is reported that the OSMT occurs in the e g -subshell at the critical temperature T c ∼ 550K, below which the conduction of electrons in the 3d x 2 −y 2 orbital is disturbed by the Hund coupling with the localized electrons in the 3d 3z 2 −r 2 orbital. 56) These experimental findings have stimulated theoretical investigations of the Mott transitions in the multiorbital systems. 8)-20), 41), 52), 54) In this paper, we give a brief review of our recent studies 14), 15), 20), 33), 36), 40) on the Mott transitions in the two-orbital Hubbard model by means of DMFT and the self-energy functional approach (SFA). 57) In particular, we focus on the role of the orbital degrees of freedom to discuss the stability of the metallic state at zero and finite temperatures. The paper is organized as follows. In §2, we introduce the model

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Phase Diagram of Orbital-Selective Mott Transitions at Finite Temperatures

Abstract: Fig. 6. Overall picture for the coexistence regions with a systematic change of J: two types of the regions are shown for J ¼ 0:25U, J ¼ 0:1U, J ¼ 0:03U and J ¼ 0 from left to right. At J ¼ 0, the transition from the metal to OSM disappears.

Cited by 23 publications

References 44 publications

Thermodynamic properties of the two-orbital Hubbard model

Thermodynamic properties of the two-orbital Hubbard model

Multisite versus multiorbital Coulomb correlations studied within finite-temperature exact diagonalization dynamical mean-field theory

Mott Transitions in Two-Orbital Hubbard Systems

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