Superconductivity from Emerging Magnetic Moments

Hoshino, Shintaro; Werner, Philipp

doi:10.1103/physrevlett.115.247001

Cited by 121 publications

(198 citation statements)

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“…For a fixed total occupation of a given site, the interaction J differentiates between the energies of different orbital occupation and spin states. In a lattice environment, this can lead to considerable shifts in the metal-Mott insulator phase boundaries [2,3], to local moment formation [4], nonlocal correlation effects [5,6], and various types of symmetry breaking [7][8][9][10][11][12][13]. Already in the two-band case, nontrivial crossovers and phase transitions can be observed.…”

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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confidence: 99%

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

et al. 2016

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“…In particular, we demonstrated a novel mechanism for photoenhanced excitonic order based on a cooperative effect between the e-ph coupling, the massive phase mode, and the Hartree shift. Combining photoexcitation and a reduction of the symmetry of the Hamiltonian may provide a new strategy to enhance analogous orders such as SC [58].…”

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Photoinduced Enhancement of Excitonic Order

et al. 2017

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We study the dynamics of excitonic insulators coupled to phonons using the time-dependent mean-field theory. Without phonon couplings, the linear response is given by the damped amplitude oscillations of the order parameter with a frequency equal to the minimum band gap. A phonon coupling to the interband transfer integral induces two types of long-lived collective oscillations of the amplitude, one originating from the phonon dynamics and the other from the phase mode, which becomes massive. We show that, even for small phonon coupling, a photoinduced enhancement of the exciton condensation and the gap can be realized. Using the Anderson pseudospin picture, we argue that the origin of the enhancement is a cooperative effect of the massive phase mode and the Hartree shift induced by the photoexcitation. We also discuss how the enhancement of the order and the collective modes can be observed with time-resolved photoemission spectroscopy. [7][8][9][10][11][12]. An EI state is formed by the macroscopic condensation of electron-hole pairs [13,14], and its theoretical description is analogous to the BCS or Bose-Einstein condensate (BEC) theory for SC. Although the idea of exciton condensation was proposed already in the 1960s [13][14][15], the interest in this topic has been renewed recently by the study of some candidate materials such as 1T-TiSe 2 and Ta 2 NiSe 5 (TNS) [16][17][18][19][20][21]. Their analogy to SC makes the EI an interesting system for nonequilibrium studies. In particular, for TNS, time-and angle-resolved photoemission spectroscopy (trARPES) experiments showed that the direct band gap can be either decreased or increased depending on the pump fluence [11], which was interpreted in terms of a photoinduced enhancement or suppression of excitonic order. A more recent report of the amplitude mode [12] provides further confirmation of an EI state in TNS.So far, the theoretical works on EIs have mainly focused on the equilibrium properties such as the BEC-BCS crossover [22,23], the coupling of the EI to phonons [24][25][26], linear susceptibilities [27][28][29], and the effect of strong interactions and new emergent phases [30][31][32]. In contrast, the nonequilibrium investigation of EIs has just begun [10]. In this work, using TNS as a model system, we clarify two basic effects of the electron-phonon (e-ph) coupling on the dynamics of EIs: (i) the effect on collective modes and (ii) the impact on the excitonic order after

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“…S3(d) in [26]). A recent study [25] has shown that in the case of a multiorbital Hubbard model without spin-orbit coupling, s-wave spin-triplet superconductivity can appear along the spin-freezing line. The effect of the spin-orbital cross-correlation on this superconductivity will be an interesting future research topic.…”

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J Freezing and Hund’s Rules in Spin-Orbit-Coupled Multiorbital Hubbard Models

et al. 2017

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We investigate the phase diagram of the spin-orbit-coupled three orbital Hubbard model at arbitrary filling by means of dynamical mean-field theory combined with continuous-time quantum Monte Carlo. We find that the spin-freezing crossover occurring in the metallic phase of the nonrelativistic multiorbital Hubbard model can be generalized to a J-freezing crossover, with J = L+S, in the spin-orbit-coupled case. In the J-frozen regime the correlated electrons exhibit a non-trivial flavor selectivity and energy dependence. Furthermore, in the regions near n = 2 and n = 4 the metallic states are qualitatively different from each other, which reflects the atomic Hund's third rule. Finally, we explore the appearance of magnetic order from exciton condensation at n = 4 and discuss the relevance of our results for real materials.PACS numbers: 71.10. Hf, 71.15.Rf, 71.30.+h, 75.25.Dk Introduction. In 4d and 5d transition metal oxides the interplay and competition between kinetic energy, spinorbit coupling (SOC) and correlation effects results in several interesting phenomena, such as spin-orbit assisted Mott transitions [1][2][3][4][5][6], unconventional superconductivity [9, 10], topological phases [11], exciton condensation [10, 12,13], or exotic magnetic orders [14,15]. Transition metal oxides involving 4d and 5d electrons show diverse structures like the Ruddlesden-Popper series [1, 9], double perovskite, [14][15][16] two-dimensional honeycomb geometry [3][4][5][6][7][8] or pyrochlore lattices [17]. In an octahedral environment, as in most of the 4d and 5d materials mentioned above, the five d orbitals are split into low energy t 2g and higher energy e g levels. The SOC further splits the low energy t 2g levels into a so-called j = 1/2 doublet and j = 3/2 quadruplet. The energy separation between the j = 1/2 and j = 3/2 bands is proportional to the strength of the SOC. Existing ab-initio density functional theory calculations [17,18] suggest that in some materials a multiorbital description including both the j = 1/2 and j = 3/2 subbands should be considered.Most theoretical studies of 4d and 5d systems have focused on material-specific models with fixed electronic filling. Here we follow a different strategy and explore the possible states that emerge from a multiband Hubbard model with spin-orbit coupling at arbitrary filling. This allows us to investigate unexplored regions in parameter space which may exhibit interesting phenomena. Specifically, by performing a systematic analysis of the local J moment susceptibility (J = L + S) as a function of Coulomb repulsion U , Hund's coupling J H , spin-orbit coupling λ and filling n, we identify Mott-Hubbard insulating phases and complex metallic states. We find a J-freezing crossover between a Fermi liquid (FL) and a non-Fermi liquid (NFL) phase where the latter shows a distinct flavor selectivity that originates from the SOC. In addition, we observe a strong asymmetry in the metallic phase between filling n = 2 and n = 4 with properties reminiscent of the atomic Hund'...

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Superconductivity from Emerging Magnetic Moments

Cited by 121 publications

References 40 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

Photoinduced Enhancement of Excitonic Order

J Freezing and Hund’s Rules in Spin-Orbit-Coupled Multiorbital Hubbard Models

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