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

Steiner, Karim; Hoshino, Shintaro; Nomura, Yusuke; Werner, Philipp

doi:10.1103/physrevb.94.075107

Cited by 32 publications

(37 citation statements)

References 38 publications

(86 reference statements)

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“…Evidently, the SC dome is peaked in the region of maximum orbital fluctuations. In this sense, the intraorbital spin-singlet pairing in fulleride compounds is the negative-J analogue of the recently discussed fluctuating local spin-moment induced spin-triplet superconductivity in multiorbital systems with J > 0 [30,31]. More explicitly, the originally repulsive intra-orbital interaction U can become attractive by considering the second-order perturbation contribution,…”

Section: 8 Imentioning

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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Section: 8 Imentioning

confidence: 99%

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

Hoshino¹,

Werner²

2017

Phys. Rev. Lett.

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“…Since alkali doped fullerides are multiorbital systems and an effective negative Hund's coupling from the Jahn-Teller screening plays an important role [56][57][58][59], we need to go beyond the Holstein model to fully understand the mechanism.…”

Section: Discussionmentioning

confidence: 99%

Nonequilibrium steady states and transient dynamics of conventional superconductors under phonon driving

Murakami¹,

Tsuji²,

Eckstein³

et al. 2017

Phys. Rev. B

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154

138

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We perform a systematic analysis of the influence of phonon driving on the superconducting Holstein model coupled to heat baths by studying both the transient dynamics and the nonequilibrium steady state (NESS) in the weak and strong electron-phonon coupling regimes. Our study is based on the nonequilibrium dynamical mean-field theory, and for the NESS we present a Floquet formulation adapted to electron-phonon systems. The analysis of the phonon propagator suggests that the effective attractive interaction can be strongly enhanced in a parametric resonant regime because of the Floquet side bands of phonons. While this may be expected to enhance the superconductivity (SC), our fully self-consistent calculations, which include the effects of heating and nonthermal distributions, show that the parametric phonon driving generically results in a suppression or complete melting of the SC order. In the strong coupling regime, the NESS always shows a suppression of the SC gap, the SC order parameter, and the superfluid density as a result of the driving, and this tendency is most prominent at the parametric resonance. Using the real-time nonequilibrium DMFT formalism, we also study the dynamics towards the NESS, which shows that the heating effect dominates the transient dynamics, and SC is weakened by the external driving, in particular at the parametric resonance. In the weak coupling regime, we find that the SC fluctuations above the transition temperature are generally weakened under the driving. The strongest suppression occurs again around the parametric resonances because of the efficient energy absorption.

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“…V A). Through the intra-molecular pair-hopping term H ph , this pair is delocalised between any of the three orbitals, and these orbital fluctuations promote SC [19,22].…”

Section: A Inverted-hund Model and Strongly-correlated Superconductimentioning

confidence: 99%

“…Even though the gap symmetry is s-wave, the mechanism of SC has been the subject of much debate. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Indeed, the narrow bandwidth (W ∼0.5 eV), the intramolecular Coulomb interaction (U ∼0.6 eV), and the typical frequency of the relevant intramolecular Jahn-Teller phonons (ω ph ∼0.1 eV) are comparable energy scales, which raises questions about the validity of conventional phonon-mediated SC mechanisms [3,5,23,24].…”

Section: Introductionmentioning

confidence: 99%

Enhancing superconductivity inA3C60fullerides

et al. 2016

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Motivated by the recent experimental report of a possible light-induced superconductivity in K3C60 at high temperature [Mitrano et al., Nature 530, 451 (2016)], we investigate theoretical mechanisms for enhanced superconductivity in A3C60 fullerenes. We find that an 'interaction imbalance' corresponding to a smaller value of the Coulomb matrix element for two of the molecular orbitals in comparison to the third one, efficiently enhances superconductivity. Furthermore, we perform firstprinciple calculations of the changes in the electronic structure and in the screened Coulomb matrix elements of K3C60 , brought in by the deformation associated with the pumped T1u intra-molecular mode. We find that an interaction imbalance is indeed induced, with a favorable sign and magnitude for superconductivity enhancement. The physical mechanism responsible for this enhancement consists in a stabilisation of the intra-molecular states containing a singlet pair, while preserving the orbital fluctuations allowing for a coherent inter-orbital delocalization of the pair. Other perturbations have also been considered and found to be detrimental to superconductivity. The light-induced deformation and ensuing interaction imbalance is shown to bring superconductivity further into the strong-coupling regime.

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

Cited by 32 publications

References 38 publications

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

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

Nonequilibrium steady states and transient dynamics of conventional superconductors under phonon driving

Enhancing superconductivity inA3C60fullerides

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