Superconductivity in the two-band Hubbard model

Koga, Akihisa; Werner, Philipp

doi:10.1103/physrevb.91.085108

Cited by 32 publications

(39 citation statements)

References 42 publications

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“…This superconducting phase borders an antiferromagnetic phase near half filling, and in the doped system a ferromagnetic phase at large U . Intraorbital spin-singlet pairing occurs in models with a negative J [19,20].…”

Section: Introductionmentioning

confidence: 99%

Long-range orders and spin/orbital freezing in the two-band Hubbard model

et al. 2016

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We solve the orbitally degenerate two-band Hubbard model within dynamical mean field theory and map out the instabilities to various symmetry-broken phases based on an analysis of the corresponding lattice susceptibilities. Phase diagrams as a function of the Hund coupling parameter J are obtained both for the model with rotationally invariant interaction and for the model with Ising-type anisotropy. For negative J , an intraorbital spin-singlet superconducting phase appears at low temperatures, while the normal state properties are characterized by an orbital-freezing phenomenon. This is the negative-J analog of the recently discovered fluctuating-moment induced s-wave spin-triplet superconductivity in the spin-freezing regime of multiorbital models with J > 0.

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Section: Introductionmentioning

confidence: 99%

Long-range orders and spin/orbital freezing in the two-band Hubbard model

et al. 2016

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“…Orbital γ = 3 behaves as a Fermi liquid (Im Σ(ε n → 0) → 0), while the self energies of the other orbitals diverge at low frequency, indicating a Mott insulating behavior. From studies of the Hubbard model [27], it is known that such a divergence of the self-energy is a characteristic feature of localized or paired electrons [15,29,33]. A schematic illustration for the SOSM state …”

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confidence: 99%

Spontaneous Orbital-Selective Mott Transitions and the Jahn-Teller Metal of A3C60

Hoshino¹,

Werner²

2017

Phys. Rev. Lett.

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The alkali-doped fullerides A3C60 are half-filled three-orbital Hubbard systems which exhibit an unconventional superconducting phase next to a Mott insulator. While the pairing is understood to arise from an effectively negative Hund coupling, the highly unusual Jahn-Teller metal near the Mott transition, featuring both localized and itinerant electrons, has not been understood. This property is consistently explained by a previously unrecognized phenomenon: the spontaneous transition of multiorbital systems with negative Hund coupling into an orbital-selective Mott state. This symmetry-broken state, which has no ordinary orbital moment, is characterized by an orbitaldependent two-body operator (the double occupancy) or an orbital-dependent kinetic energy, and may be regarded as a diagonal-order version of odd-frequency superconductivity. We propose that the recently discovered Jahn-Teller metal phase of RbxCs3−xC60 is an experimental realization of this novel state of matter.The appearance of long-range order by spontaneous symmetry breaking (SSB) is a fundamental and widely studied concept in physics. In condensed matter systems, the ordered state is typically characterized by an order parameter measuring the charge, magnetic moment, orbital angular momentum, or the pair amplitude in a superconductor. There may however exist more complex types of ordering phenomena. Here we demonstrate that in a certain class of multi-orbital systems one observes an orbital symmetry breaking into a state without conventional order parameter, but with an orbital-dependent double occupancy (a composite order parameter) and an orbital-dependent kinetic energy. The resulting ordered phase is a spontaneous orbital-selective Mott (SOSM) state, in which itinerant and localized electrons coexist. As this state combines properties of the metal (connected to the weak-interaction limit) and Mott insulator (connected to the strong-interaction limit) it cannot be detected by perturbative methods from either limits, and its study requires the use of sophisticated techniques. The ordering phenomenon can be discussed in terms of a symmetry-breaking field or order parameter with odd time (frequency) dependence, and is hence related to the concept of odd-frequency superconductivity [1-4].We will argue that this unconventional SOSM state is realized in alkali-doped fullerides [5][6][7][8][9][10][11][12][13], which are promising candidates for diagonal odd-frequency orders. Several compounds in this class of materials can be regarded as strongly correlated systems since a Mott transition occurs as a function of pressure. In the case of an fcc lattice [12], the Mott insulator stays paramagnetic in a wide range of temperature due to geometrical frustration, while it is antiferromagnetically ordered in the case of a bcc lattice, which is bipartite [11]. With increasing pressure, the system turns into a paramagnetic metal and is unstable to superconductivity below a maximum T c ≃ 38 K [11]. Recently, a so-called Jahn-Teller metal (JTM) state has bee...

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“…Apart from superconductivity in the attractive [44][45][46][47][48][49][50] and multiband [51][52][53][54] Hubbard models DMFT investigations of longrange ordered states other than magnetically ordered phases are rare. We note that superconductivity in repulsive Hubbard model was extensively studied [55][56][57] with cluster extensions of DMFT [58].…”

Section: Methodsmentioning

confidence: 99%

LDA+DMFT approach to ordering phenomena and the structural stability of correlated materials

Kuneš

Leonov

Augustinský

et al. 2017

Eur. Phys. J. Spec. Top.

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Abstract. Materials with correlated electrons often respond very strongly to external or internal influences, leading to instabilities and states of matter with broken symmetry. This behavior can be studied theoretically either by evaluating the linear response characteristics, or by simulating the ordered phases of the materials under investigation. We developed the necessary tools within the dynamical mean-field theory (DMFT) to search for electronic instabilities in materials close to spin-state crossovers and to analyze the properties of the corresponding ordered states. This investigation, motivated by the physics of LaCoO 3, led to a discovery of condensation of spinful excitons in the two-orbital Hubbard model with a surprisingly rich phase diagram. The results are reviewed in the first part of the article. Electronic correlations can also be the driving force behind structural transformations of materials. To be able to investigate correlation-induced phase instabilities we developed and implemented a formalism for the computation of total energies and forces within a fully charge self-consistent combination of density functional theory and DMFT. Applications of this scheme to the study of structural instabilities of selected correlated electron materials such as Fe and FeSe are reviewed in the second part of the paper.

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Superconductivity in the two-band Hubbard model

Cited by 32 publications

References 42 publications

Long-range orders and spin/orbital freezing in the two-band Hubbard model

Long-range orders and spin/orbital freezing in the two-band Hubbard model

Spontaneous Orbital-Selective Mott Transitions and the Jahn-Teller Metal of A3C60

LDA+DMFT approach to ordering phenomena and the structural stability of correlated materials

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