Strong Coupling Nature of the Excitonic Insulator State in 
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Sugimoto, K.; Nishimoto, Sei‐ichi; Kaneko, Tatsuya; Ohta, Y.

doi:10.1103/physrevlett.120.247602

Cited by 99 publications

(80 citation statements)

References 38 publications

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“…This is because the binding energy of excitons is two orders of magnitude greater than that of Cooper pairs in BCS superconductors. However, a very recent paper proposed the possibility of a small-gap semiconducting phase above the transition temperature due to preformed excitons in spite of the non-interacting semimetallic bands in Ta 2 NiSe 5 [49]. Nevertheless, one of our main observations, the orbital character inversion that is the hallmark of a semimetallic non-interacting band, is consistent with this recent paper.…”

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confidence: 91%

Strong interband interaction in the excitonic insulator phase of Ta2NiSe5

et al. 2019

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Excitonic insulator (EI) was proposed in 60's as a distinct insulating state originating from pure electronic interaction, but its material realization has been elusive with extremely few material candidates and with only limited evidence such as anomalies in transport properties, band dispersions, or optical transitions. We investigate the real-space electronic states of the low temperature phase in Ta2NiSe5 with an atomic resolution to clearly identify the quasiparticle energy gap together with the strong electron-hole band renormalization using scanning tunneling microscopy (STM) and spectroscopy (STS). These results are in good agreement with the EI transition scenario in Ta2NiSe5. Our spatially-resolved STS data and theoretical calculations reveal further the orbital inversion at band edges, which indicates the exciton condensation close to the Bardeen-Cooper-Schrieffer regime. arXiv:1811.01552v1 [cond-mat.mtrl-sci]

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confidence: 91%

Strong interband interaction in the excitonic insulator phase of Ta2NiSe5

et al. 2019

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“…In other words, the use of lower-energy laser lights may be more informative to clarify the nonequilibrium dynamics of Ta 2 NiSe 5 in the lowest energy scales. Also, it was pointed out that Ta 2 NiSe 5 is in the strong coupling BEC regime, despite the fact that the noninteracting band structure is semimetallic [47]. Such a situation cannot be treated in our simple mean-field approximation.…”

Section: Summary and Discussionmentioning

confidence: 91%

Nonequilibrium dynamics in the pump-probe spectroscopy of excitonic insulators

2018

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We study the nonequilibrium dynamics in the pump-probe spectroscopy of excitonic insulators using the spinless two-orbital model with phonon degrees of freedom in the time-dependent meanfield approximation. We introduce the pulse light as a time-dependent vector potential via the Peierls phase in the Hamiltonian. We find that, in the Bose-Einstein condensation regime where the normal state is semiconducting, the excitonic order is suppressed when the frequency of the pulse light is slightly larger than the band gap, while the order is enhanced when the frequency of the pulse is much larger than the band gap. We moreover find that the excitonic order is completely destroyed in the former situation if the intensity of the pulse is sufficiently strong. In the BCS regime where the normal state is semimetallic, we find that the excitonic order is always suppressed, irrespective of the frequency of the pulse light. The quasiparticle band structure and optical conductivity spectrum after the pumping are also calculated for the instantaneous states.

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“…Note that the number N α of electrons for each orbital α (= 1, 2) is conserved even in the presence of the external field in Eq. (18). N α depends on the values of D and U .…”

Section: Methodsmentioning

confidence: 99%

“…At half filling, i.e., N 1 +N 2 = L, the ground state of the EFKM for large U is an insulator [see Fig. 1(b)] with the strong excitonic correlation [18]. Note that, when t…”

Section: Modelmentioning

confidence: 99%

“…The excitonic order is described as a quantum condensed state of electron-hole pairs (or excitons) via interband Coulomb interactions [1][2][3], and the insulator realized by the excitonic order or strong excitonic correlation is called the excitonic insulator. As the promising candidates among transition-metal compounds, the possible realization of spin-singlet excitonic phase has been suggested in the transition-metal chalcogenides 1T -TiSe 2 [7][8][9][10][11][12] and Ta 2 NiSe 5 [13][14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

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Photoinduced electron-electron pairing in the extended Falicov-Kimball model

et al. 2019

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By employing the time-dependent exact diagonalization method, we investigate the photoexcited states of the excitonic insulator in the extended Falicov-Kimball model (EFKM). We here show that the pulse irradiation can induce the interband electron-electron pair correlation in the photoexcited states, while the excitonic electron-hole pair correlation in the initial ground state is strongly suppressed. We also show that the photoexcited states contains the eigenstates of the EFKM with a finite number of interband electron-electron pairs, which are responsible for the enhancement of the electron-electron pair correlation. The mechanism found here is due to the presence of the internal SU(2) pairing structure in the EFKM and thus it is essentially the same as that for the photoinduced η-pairing in the repulsive Hubbard model reported recently [T. Kaneko et al., Phys. Rev. Lett. 122, 077002 (2019)]. This also explains why the nonlinear optical response is effective to induce the electron-electron pairs in the photoexcited states of the EFKM. Furthermore, we show that, unlike the η-pairing in the Hubbard model, the internal SU(2) structure is preserved even for a nonbipartite lattice when the EFKM has the direct-type band structure, in which the pulse irradiation can induce the electron-electron pair correlation with momentum q = 0 in the photoexcited states. We also discuss briefly the effect of a perturbation that breaks the internal SU(2) structure.

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Strong Coupling Nature of the Excitonic Insulator State in Ta2NiSe5

Cited by 99 publications

References 38 publications

Strong interband interaction in the excitonic insulator phase of Ta2NiSe5

Strong interband interaction in the excitonic insulator phase of Ta2NiSe5

Nonequilibrium dynamics in the pump-probe spectroscopy of excitonic insulators

Photoinduced electron-electron pairing in the extended Falicov-Kimball model

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