Antiferroelectric distortion with anomalous phonon softening in the excitonic insulator 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Ta</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>NiSe</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:mrow></mml:math>

Nakano, Ayako; Hasegawa, Tetsuya; Tamura, Shun; Katayama, Naoyuki; Tsutsui, Satoshi; Sawa, Hiroshi

doi:10.1103/physrevb.98.045139

Cited by 71 publications

(85 citation statements)

References 40 publications

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“…Singlecrystalline samples with a typical size of 0.04 × 1 × 10 mm 3 were obtained in the cooler end. Density functional theory and the projector augmented wave method implemented in VASP [25][26][27][28][29][30] were used for band structure calculations in the monoclinic phase with experimentally determined structural parameters [31]. The kinetic energy cutoff of the plane-wave basis was 500 eV, and the Brillouin zone integration was performed using a 11 × 11 × 5 k-point grid.…”

Section: Methodsmentioning

confidence: 99%

Mapping the unoccupied state dispersions in Ta2NiSe5 with resonant inelastic x-ray scattering

et al. 2020

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The transition metal chalcogenide Ta 2 NiSe 5 undergoes a second-order phase transition at T c = 328 K involving a small lattice distortion. Below T c , a band gap at the center of its Brillouin zone increases up to about 0.35 eV. In this work, we study the electronic structure of Ta 2 NiSe 5 in its low-temperature semiconducting phase, using resonant inelastic x-ray scattering (RIXS) at the Ni L 3 edge. In addition to a weak fluorescence response, we observe a collection of intense Raman-like peaks that we attribute to electron-hole excitations. Using density functional theory calculations of its electronic band structure, we identify the main Raman-like peaks as interband transitions between valence and conduction bands. By performing angle-dependent RIXS measurements, we uncover the dispersion of these electron-hole excitations that allows us to extract the low-energy boundary of the electron-hole continuum. From the dispersion of the valence band measured by angle-resolved photoemission spectroscopy, we derive the effective mass of the lowest unoccupied conduction band.

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Section: Methodsmentioning

confidence: 99%

Mapping the unoccupied state dispersions in Ta2NiSe5 with resonant inelastic x-ray scattering

et al. 2020

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“…The realistic models for possible excitonic materials should have the spin degrees of freedom, and thus our theory has to be extended to a spinful model such as the two-band Hubbard model [78][79][80][81]. Furthermore, the importance of the electron-phonon coupling has been pointed out in the excitonic candidate materials TiSe 2 and Ta 2 NiSe 5 [82][83][84]. Therefore, in order to understand the pump-probe experiments reported recently in these materials, the phonon degrees of freedom are also important in the theory.…”

Section: Resultsmentioning

confidence: 99%

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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“…ARPES experiments revealed a flattening of the valence band when cooling below the transition temperature [11,12], which has been taken as indication of an EI state within a model simulation [13]. Motivated by this, various experiments have recently performed for this material, using NMR [14], inelastic xray scattering [15], scanning tunneling microscopy or spectroscopy [16,17], and time-and angle-resolved photoemission spectroscopy (t-ARPES) [18][19][20]. Besides there is the isostructual compound Ta 2 NiS 5 , which opens up the possibility to perform comparative measurements and analysis, not only of the photoemission [21] but also of the magnetic susceptibility [10] and the optical conductivity [22,23].…”

Section: Introductionmentioning

confidence: 95%

Finite-temperature photoemission in the extended Falicov-Kimball model: a case study for Ta$_2$NiSe$_5$

Lange

Fehske

2021

SciPost Phys.

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Utilizing the unbiased time-dependent density-matrix renormalization group technique, we examine the photoemission spectra in the extended Falicov-Kimball model at zero and finite temperatures, particularly with regard to the excitonic insulator state most likely observed in the quasi-one-dimensional material Ta_22NiSe_55. Working with infinite boundary conditions, we are able to simulate all dynamical correlation functions directly in the thermodynamic limit. For model parameters best suited for Ta_22NiSe_55 the photoemission spectra show a weak but clearly visible two-peak structure, around the Fermi momenta k\simeq\pm k_{F}k≃±kF, which suggests that Ta_22NiSe_55 develops an excitonic insulator of BCS-like type. At higher temperatures, the leakage of the conduction-electron band beyond the Fermi energy becomes distinct, which provides a possible explanation for the bare non-interacting band structure seen in time- and angle-resolved photoemission spectroscopy experiments.

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Antiferroelectric distortion with anomalous phonon softening in the excitonic insulator Ta2NiSe5

Cited by 71 publications

References 40 publications

Mapping the unoccupied state dispersions in Ta2NiSe5 with resonant inelastic x-ray scattering

Mapping the unoccupied state dispersions in Ta2NiSe5 with resonant inelastic x-ray scattering

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

Finite-temperature photoemission in the extended Falicov-Kimball model: a case study for Ta$_2$NiSe$_5$

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