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Exciton photoemission from a ground state of a solid Ta2Pd3Te5

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Pith's one-line read The paper reports direct photoemission evidence for spontaneously formed excitons in the insulating ground state of the bulk crystal Ta2Pd3Te5, with binding energy exceeding the single-particle band gap.

desk verdict First direct photoemission evidence for a ground-state exciton in a bulk solid, pending proper control of the second-BZ subtraction. read the letter →

arxiv 2507.16453 v1 pith:NNJQ6CS7 submitted 2025-07-22 cond-mat.str-el

Siwon Lee , Kyung-Hwan Jin , SeongJin Kwon , Hyunjin Jung , Choongjae Won , Sang-Wook Cheong , Gil Young Cho , Jaeyoung Kim
show 1 more author
Han Woong Yeom
This is my paper · ORCID
classification cond-mat.str-el PACS 71.35.-y79.60.-i
keywords excitonicinsulatorTa2Pd3Te5excitonphotoemissionangle-resolvedspectroscopyodd-paritymetal-insulatortransition1swavefunctionBohrradius
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

Excitons—bound pairs of an electron and a hole—have long been predicted to form spontaneously in the ground state of a narrow-gap solid, but direct spectroscopic evidence in a three-dimensional crystal has been missing. The paper reports such evidence in Ta2Pd3Te5, a layered material that undergoes a metal-insulator transition at 365 K with almost no structural distortion. Using angle-resolved photoemission spectroscopy (ARPES) with orbital-selective light polarization, the authors isolate a non-dispersing photoemission feature at the Brillouin zone center that sits below the valence band maximum, meaning the exciton binding energy exceeds the single-particle band gap and can drive the phase transition. They extract a 1s-like exciton wavefunction with a Bohr radius near 14 Å and find the feature has odd parity in one mirror plane, which they attribute to interband hybridization between valence and conduction bands in the excitonic insulating state. If correct, this is the first direct photoemission observation of excitons in the ground state of a bulk crystalline solid.

What carries the argument

The load-bearing object is the exciton photoemission spectral function, which in the low-temperature, zero-center-of-mass limit reduces to $P(k) \propto |\varphi_{1s}(k)|^2 = 1/[1 + k^2 a_0^2/4]^4$, directly relating ARPES intensity to the squared exciton envelope wavefunction in momentum space. It comes from the convolution of the exciton wavefunction with conduction-band photoemission matrix elements, with the matrix element taken as constant. This formula carries the identification: fitting the momentum distribution curves of the subtracted feature yields the Bohr radius and confirms a 1s envelope, while the energy distribution curves yield the exciton binding energy. The second essential element is the orbital-selective dipole selection rule: comparing xz- and yz-polarized spectra distinguishes the parity of the wavefunction and identifies the odd-parity valence orbital contribution through interband hybridization.

What would settle it

Calculate the one-step ARPES intensity for the first and second Brillouin zones from the DFT band structure at the same photon energy and polarization; if the calculated first-zone/second-zone intensity ratio is not constant over the momentum-energy window used for subtraction, the residual peak is at least partly a subtraction artifact. Experimentally, repeat the measurement at different photon energies (for instance 6 eV or 21 eV) and above Tc at 400 K; a feature that changes shape or survives in the metallic phase would not be tied to the excitonic ground state.

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Extended reading notes

Core claim

The central discovery is a stationary, roughly egg-shaped photoemission signal at the Brillouin zone center of Ta2Pd3Te5 in its low-temperature insulating phase, at a binding energy of about 0.115 eV (80 K), which lies below the valence band maximum at about 0.08 eV. The signal is absent in the second Brillouin zone, where only the bare valence bands appear, and it deviates from the calculated and measured valence band dispersions. Subtracting the second-zone spectrum from the first-zone spectrum yields a residual intensity that is fit quantitatively by the exciton photoemission formula with a 1s envelope, $P(k) \propto 1/[1 + k^2 a_0^2/4]^4$, giving anisotropic Bohr radii of about 13.6 Å along Γ−Y and 15.1 Å along Γ−X. The feature is observed for xz- and x-polarized light but suppressed for yz-polarized light; the authors read this as odd parity along the yz mirror plane, involving an odd-parity component of the valence band through interband hybridization expected in an excitonic insulator. The exciton peak shifts and transfers weight with temperature in parallel with the gap opening, and it remains below the valence band top over the whole measured range below Tc, so the authors conclude the exciton binding energy exceeds the gap and drives the metal-insulator transition.

Load-bearing premise

The argument assumes that the second-Brillouin-zone ARPES spectrum can be normalized and subtracted from the first-zone spectrum to expose the exciton signal, so that any difference in photoemission matrix elements, final-state effects, or surface contributions between the two zones does not create the residual feature.

Editorial extensions

If this is right

  • The insulating state of Ta2Pd3Te5 below 365 K is an excitonic insulator: the observed bound exciton sits below the valence band maximum, so its formation energy exceeds the single-particle gap and can open the gap without relying on a lattice-driven mechanism.
  • The exciton wavefunction parameters—a 1s envelope with Bohr radii near 14 Å and a binding energy near 0.1 eV—become direct experimental targets for first-principles calculations; the existing monolayer tight-binding calculation predicts roughly twice the radius, pointing to where theory must be refined.
  • The odd-parity exciton symmetry, paired with the system's topological band structure, puts Ta2Pd3Te5 within reach of predictions of topological excitonic condensates and related exotic ground states.
  • Because the transition has an undetectably small structural distortion, Ta2Pd3Te5 provides a cleaner platform than earlier candidates for studying the crossover from preformed incoherent excitons to a condensed excitonic ground state in a bulk solid.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • Inference: If the odd-parity assignment is right, the same exciton should be nearly dark in two-photon absorption, which couples to even-parity states; a clear optical two-photon resonance would therefore test the parity conclusion independently of photoemission.
  • Inference: The subtraction procedure assumes the second-Brillouin-zone spectrum is a clean proxy for the bare valence band. A one-step photoemission calculation of matrix elements in both zones would settle whether the extracted Bohr radius and binding energy are robust; the authors do not report such a calculation.
  • Inference: The contrast with Ta2NiSe5—where exciton photoemission appears only above Tc—suggests the two materials sit on opposite sides of the BEC-BCS crossover of the excitonic transition, with Ta2Pd3Te5 in the condensed regime and Ta2NiSe5 in the preformed-exciton regime.
  • Inference: The temperature-dependent broadening of the exciton peak could be compared with a phonon-scattering model; if the width tracks a single optical phonon energy, it would provide a quantitative measure of the exciton-phonon coupling that currently limits the interpretation.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

4 major / 5 minor

Summary. The paper reports angle-resolved photoemission spectroscopy (ARPES) measurements on Ta2Pd3Te5 below its metal-insulator transition at Tc = 365 K, claiming the observation of a nondispersive photoemission feature at the Brillouin zone center with binding energy 0.115 eV at 80 K. The authors interpret this feature as direct photoemission from spontaneously formed excitons in the insulating ground state, extract a 1s-like exciton envelope with Bohr radius ~13.6–15.1 Å, and infer an odd-parity exciton wavefunction from polarization-dependent measurements. They argue that the exciton binding energy exceeds the single-particle band gap, driving the transition, and support this with a two-band mean-field model and phonon-replica simulations.

Significance. If the interpretation is correct, this would be a landmark observation: direct evidence of excitons in the ground state of a three-dimensional excitonic insulator, providing real-space wavefunction information and parity symmetry. The paper is timely and relevant to the long-standing search for excitonic insulators. The main strengths are the unusually clean temperature-dependent data, the use of orbital-selective polarization, and the attempt to rule out electron-phonon and density-wave explanations through supplemental simulations. However, the central claim rests on a subtraction procedure and peak-decomposition whose robustness is not fully demonstrated, and the quantitative agreement with the exciton photoemission model is partly a fitting exercise rather than an independent prediction.

major comments (4)
  1. [Main text, Fig. 1e and Supplemental Sec. S9] The isolation of the claimed exciton feature relies on subtracting ARPES spectra of the first Brillouin zone by those of the second zone, described as 'after normalization,' but the normalization procedure is not specified anywhere. The intensity scale, k-dependent alignment, and any energy-dependent correction between the two zones are not given. Since the valence band has a strong maximum at Γ, any zone-dependent matrix-element, final-state, or surface contribution will produce a residual concentrated at exactly the momentum where the claimed peak sits. The statement that the feature 'disappears completely in the second BZ' does not validate the baseline, because the second-zone spectrum is the baseline. Please provide the explicit normalization (e.g., integrated-energy window, valence-band intensity, or a scaling coefficient) and a control analysis showing that the residual is robust to reasonable variations in the normalization, or a comparison with a calculated k-dependent matrix-element ratio.
  2. [Fig. 3c and Supplemental Tables V–VII] The claim that the exciton lies 0.037 eV below the valence band maximum is based on a Voigt decomposition in which the exciton peak (0.115 eV) is separated from the VB1 peak (0.078 eV) by less than the fitted full-width at half-maximum of each peak (0.058–0.060 eV). With the given linewidths, the exciton peak is not resolved from the valence band; its position and intensity are strongly correlated with the tails of VB1 and VB2. The residual fit in Table VII still contains significant VB2 intensity (0.20), further complicating the decomposition. Please demonstrate the uniqueness of this decomposition, for example by fixing the valence-band parameters to those obtained from the second-zone spectrum and showing that the fit without an exciton component fails quantitatively, and by providing confidence intervals for the exciton binding energy that account for the parameter correlations.
  3. [Main text, 'polarization dependence' and Supplemental Fig. S4] The odd-parity assignment of the exciton wavefunction is asserted from the observation that the feature is visible for x-polarized but suppressed for yz-polarized photons, combined with the statement that 'the only odd parity wave function involved here is the valence Pd dxy orbital.' This conclusion requires a quantitative analysis of the exciton photoemission matrix element, including the degree of interband hybridization and the dipole matrix elements for the specific photon polarizations and final states. Without such a calculation, the polarization data could reflect matrix-element or final-state effects of the ordinary valence band rather than the parity of the exciton envelope. Please provide a matrix-element calculation or a symmetry analysis that explicitly includes the hybridized valence and conduction bands and predicts the relative intensities for x, y, and z polarizations.
  4. [Supplemental Sec. 3 and Fig. 3, Fig. 1d] There is a circularity in the quantitative agreement between the data and the 'exciton photoemission simulation.' The Bohr radius is extracted by fitting MDCs of the subtracted spectra with the 1s formula P ∝ 1/(1 + k^2 a0^2/4)^4, and then the same formula and fitted radius are used to generate the simulated spectral function shown in Fig. 1d and Fig. 3d. This demonstrates internal consistency but not that the signal is an exciton. The two-band model parameters in Fig. S8, including Δ = 40 meV, are likewise adjusted to reproduce the observed gap. Please clarify which quantities are predicted versus fitted, and discuss the factor-of-two discrepancy with the tight-binding calculation of the exciton radius in Ref. [47], which would provide a non-circular test of the interpretation.
minor comments (5)
  1. [Abstract] The sentence 'whose material realization has been elusive' is a grammatical fragment; consider revising to 'a material realization of which has remained elusive.'
  2. [Main text, second paragraph] There is a typo: 'deviates largley' should be 'deviates largely.'
  3. [Reference [50]] The phrase 'calulated desults' in the supplemental-materials link text is a typo; it should read 'calculated results.'
  4. [Introduction, comparison with Ta2NiSe5] The sentence 'the exciton photoemission signal was observed only above Tc' is confusing because the present paper reports the signal below Tc; please rephrase to clarify that this refers to the prior Ta2NiSe5 work.
  5. [Supplemental Table II] Table II lists the same direction 'Γ−X' twice; presumably the second entry should be 'Γ−Y' to match the main-text statement that the Bohr radius is larger along Γ−X than along Γ−Y.

Circularity Check

2 steps flagged · score 6.0 of 10

The 'exciton simulation' agreement is a refit of the same 1s envelope used to fit the subtracted spectra, and the mean-field 'validation' uses a hand-set Δ = 40 meV; the central detection still has independent qualitative content.

  1. fitted input called prediction [Main text (paragraphs around Figs. 1d and 3d) and Supplemental Material Sec. 3 'Fittings of exciton wavefunction'.]
    "This signal can be simulated quantitatively well by the exciton photoemission formula (Fig. 1d and Fig. 3d) with the exciton wavefunction and the valence band dispersions at the Γ point [43, 44]. The exciton wavefunction was extracted by fitting the momentum distribution curves (MDCs, Figs. 3a and 3b) of the subtracted spectra along both Γ−Y (left) and Γ−X (right). ... The wavefunction corresponds to an 1s wavefunction, which exhibits a slightly larger Bohr radius along the Γ−X direction (approximately 15.1 ˚A) than along Γ−Y (approximately 13.6 ˚A)."

    The simulation in Figs. 1d and 3d is generated from the same 1s formula, P ∝ |ϕ1s|^2 = 1/[1+k^2 a0^2/4]^4, whose only free parameter a0 was obtained by fitting the MDCs of the same subtracted spectra. The agreement between data and 'simulation' is therefore a measure of the fit quality, not an independent confirmation of the exciton interpretation. Reporting that the wavefunction 'corresponds to a 1s wavefunction' restates the fitting ansatz by construction.

  2. fitted input called prediction [Supplemental Material Sec. 5 'Two band model calculation with an excitonic interaction' and Fig. S8 caption.]
    "Model band structure after including the SOC and excitonic interaction with an order parameter of ∆ = 40meV. ... The excitonic state arises from the coupling of electron-hole pairs, leading to a significant increase in the band gap, reflecting the binding energy of the excitons (Figure S8c). These results demonstrate how many-body interactions drive the transition from the semimetallic phase to the excitonic state, thereby validating the experimental claims of a correlated ground state."

    The mean-field model's gap is generated by inserting the excitonic order parameter Δ = 40 meV by hand, along with the listed band parameters, and then the same model is used to 'validate' the experimentally observed gap. This is a demonstration that a chosen input produces a gap of the intended size, not independent evidence that the gap is excitonic in origin. The validation step reduces to a fitted input.

full rationale

The central identification is not fully circular: the flat dispersion, its absence in the second Brillouin zone, the persistence down to 10 K, the temperature-dependent spectral weight transfer, and the polarization dependence are independent qualitative observations. However, two quantitative 'confirmations' reduce to their own inputs. First, the 'quantitative simulation' of the exciton photoemission feature uses the same 1s envelope and the same fitted Bohr radii that were obtained by fitting the same subtracted MDCs, so the match is a refit rather than a prediction. Second, the two-band mean-field model inserts Δ = 40 meV by hand and then claims to validate the correlated ground state; the output gap inherits its scale from the input order parameter. The self-citation to the group's earlier Ta2NiSe5 work is not counted as circular because the underlying photoemission model [43] is independent and the prior application is externally testable. The second-BZ subtraction baseline is a notable fragility because the normalization and k-dependent matrix-element controls are not fully specified, but that is a correctness risk rather than a constructional circularity. Overall, the core observation retains independent content, but the presented quantitative validations are partially forced by their fitting inputs: score 6.

Assumptions & free parameters 6 free parameters · 6 assumptions · 0 invented entities

The central claim rests on the applicability of the exciton photoemission formula to an equilibrium condensate, on the use of a second-zone ARPES spectrum as a baseline, and on DFT-based orbital assignments. The paper introduces several fitted parameters (Bohr radii, Voigt profiles, two-band model parameters, phonon replica parameters) and relies on a mean-field treatment of the excitonic interaction, none of which is derived from first principles in this work.

free parameters (6)
  • Exciton Bohr radius a0 along Γ-Y = 13.56 ± 0.022 Å at 80 K (12.0-12.3 Å at 250-370 K)
    Fitted to the momentum distribution curves of the subtracted ARPES feature using the 1s exciton envelope 1/[1+k^2 a0^2/4]^4.
  • Exciton Bohr radius a0 along Γ-X = 15.10 ± 0.045 Å
    Fitted to the MDC along Γ-X at 80 K; the anisotropy is interpreted as reflecting the band structure.
  • Voigt fit parameters for VB1, VB2, VB3, Exciton = e.g., Exciton binding energy 0.115 eV, FWHM 0.058 eV, Lorentz/Gauss ratio 0.20, normalized intensity 0.46 (Table V)
    Used to extract peak positions and to quantify the spectral weight transfer; these parameters are fitted to the EDCs.
  • Two-band model parameters (M0, My, Mx, Ax, Ay, Cx, Cy) and order parameter Δ = M0=-0.03 eV, My=-4 eV, Mx=0.05 eV, Ax=0.007 eV, Ay=0.09 eV, Cx=0.004 eV, Cy=-0.3 eV, Δ=40 meV
    Chosen to reproduce the DFT band structure and the experimental gap; the model is then used to 'validate' the excitonic phase, which is circular.
  • Phonon replica parameters A and ℏω = A=1, ℏω=30 meV
    Adopted in the simulation of phonon-induced broadening to rule out phonon replicas; not derived from data.
  • Exciton broadening factor = proportional to kBT
    Set ad hoc in the temperature-dependent EDC fits (Fig. S13).
assumptions (6)
  • domain assumption The exciton photoemission formula of Rustagi-Kemper applies to equilibrium spontaneously formed excitons in a solid, with constant matrix element, Q=0, and w=0.
    The formula was derived for pump-probe photoemission of optically induced excitons; the paper extends it to equilibrium excitons, following the earlier Ta2NiSe5 work (Ref 44).
  • domain assumption The second Brillouin zone ARPES spectrum is an accurate bare valence band baseline.
    Underlies the subtraction in Fig. 1e; the normalization is not fully specified.
  • domain assumption The valence band near Γ is composed of Pd dxz and Te px orbitals with the stated mirror parities, as given by DFT.
    Used to interpret the polarization dependence and to conclude odd parity; relies on DFT orbital character.
  • ad hoc to paper The two-band model Hamiltonian (Eq. D2) with the chosen parameters is a sufficient representation of the low-energy physics.
    Parameters are chosen to match DFT and the experimental gap; the model is not derived from first principles.
  • domain assumption The top of the valence band has no kz dispersion, ruling out final-state broadening.
    Cited from Ref 58; used to exclude final-state effects.
  • domain assumption The standard BCS-like mean-field treatment of the excitonic interaction is valid for this material.
    Used in the supplement to compute the excitonic gap.

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Cite this review

Pith. "Pith review of Exciton photoemission from a ground state of a solid Ta2Pd3Te5." pith.science (2026). https://pith.science/paper/NNJQ6CS7

@misc{pith2026250716453,
  author       = {Pith},
  title        = {Pith review of: Exciton photoemission from a ground state of a solid Ta2Pd3Te5},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/NNJQ6CS7}},
  note         = {Machine review of arXiv:2507.16453}
}
read the original abstract

Excitons are bosonic quasiparticles with a variety of applications in optoelectronics, photosyn thesis, and dissipationless informatics, and their lifetime can become sufficiently long to form a quantum condensate. While exciton condensation has been predicted to occur as a ground state of a solid, so called an excitonic insulator, whose material realization has been elusive. Here we report the observation of direct photoemission signals from excitons in a ground state of a very recent excitonic insulator candidate Ta2Pd3Te5 below its metal-insulator transition temperature using orbital-selective angle-resolved photoemission spectroscopy. It is confirmed that the excitons have a lower energy than the valence band maximum to possibly drive the phase transition. This measurement further discloses the size and the unusual odd parity of the exciton wave function. The present finding opens an avenue toward applications of coherent excitons in solid systems and searching for exotic quantum phases of exciton condensates.

Figures

Figures reproduced from arXiv: 2507.16453 by the authors.

Figure 1
Figure 1. FIG. 1: a) An experimental setup of exciton photoemission with linearly polarized light. The squared exciton radial [PITH_FULL_IMAGE:figures/full_fig_p007_1.png] view at source ↗
Figure 2
Figure 2. FIG. 2: a) ARPES spectra taken along the Γ [PITH_FULL_IMAGE:figures/full_fig_p008_2.png] view at source ↗
Figure 3
Figure 3. FIG. 3: a) MDCs crossing the maximum spectral weights from the spectra shown in Fig. 1c (circles) are fit by the [PITH_FULL_IMAGE:figures/full_fig_p009_3.png] view at source ↗

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Works this paper leans on

81 extracted references · 76 canonical work pages

  1. [47]

    J. Yao, H. Sheng, R. Zhang, R. Pang, J.-J. Zhou, Q. Wu, H. Weng, X. Dai, Z. Fang, and Z. Wang, Excitonic insta- bility in Ta 2Pd3Te5 monolayer, Chinese Physics Letters 41, 097101 (2024)

    work page 2024

  2. [1]

    Van Amerongen, R

    H. Van Amerongen, R. Van Grondelle, et al. , Photosyn- thetic excitons (World Scientific, 2000)

    work page 2000

  3. [2]

    Brixner, J

    T. Brixner, J. Stenger, H. M. Vaswani, M. Cho, R. E. Blankenship, and G. R. Fleming, Two-dimensional spec- troscopy of electronic couplings in photosynthesis, Nature 434, 625 (2005)

    work page 2005

  4. [3]

    Kuznetsova, M

    Y. Kuznetsova, M. Remeika, A. High, A. Hammack, L. Butov, M. Hanson, and A. Gossard, All-optical ex- citonic transistor, Optics letters 35, 1587 (2010)

    work page 2010

  5. [4]

    S. M. Menke, W. A. Luhman, and R. J. Holmes, Tai- lored exciton diffusion in organic photovoltaic cells for enhanced power conversion efficiency, Nature materials 12, 152 (2013)

    work page 2013

  6. [5]

    Romero, R

    E. Romero, R. Augulis, V. I. Novoderezhkin, M. Ferretti, J. Thieme, D. Zigmantas, and R. Van Grondelle, Quan- tum coherence in photosynthesis for efficient solar-energy conversion, Nature physics 10, 676 (2014)

    work page 2014

  7. [6]

    J. S. Ross, P. Klement, A. M. Jones, N. J. Ghimire, J. Yan, D. Mandrus, T. Taniguchi, K. Watanabe, K. Ki- tamura, W. Yao, et al. , Electrically tunable excitonic light-emitting diodes based on monolayer WSe2 p–n junc- tions, Nature nanotechnology 9, 268 (2014)

    work page 2014

  8. [7]

    M. M. Furchi, A. Pospischil, F. Libisch, J. Burgdorfer, and T. Mueller, Photovoltaic effect in an electrically tun- able van der waals heterojunction, Nano letters 14, 4785 (2014)

    work page 2014

Show all 81 references
  1. [8]

    Y. Ye, Z. J. Wong, X. Lu, X. Ni, H. Zhu, X. Chen, Y. Wang, and X. Zhang, Monolayer excitonic laser, Na- ture Photonics 9, 733 (2015)

    2015

  2. [9]

    Romero, V

    E. Romero, V. I. Novoderezhkin, and R. Van Grondelle, Quantum design of photosynthesis for bio-inspired solar- energy conversion, Nature 543, 355 (2017)

    2017

  3. [10]

    Mueller and E

    T. Mueller and E. Malic, Exciton physics and device ap- plication of two-dimensional transition metal dichalco- genide semiconductors, npj 2D Materials and Applica- tions 2, 29 (2018)

    2018

  4. [11]

    J´ erome, T

    D. J´ erome, T. Rice, and W. Kohn, Excitonic insulator, Physical Review 158, 462 (1967)

    1967

  5. [12]

    Halperin and T

    B. Halperin and T. Rice, Possible anomalies at a semimetal-semiconductor transistion, Reviews of Modern Physics 40, 755 (1968)

    1968

  6. [13]

    Wakisaka, T

    Y. Wakisaka, T. Sudayama, K. Takubo, T. Mizokawa, M. Arita, H. Namatame, M. Taniguchi, N. Katayama, M. Nohara, and H. Takagi, Excitonic insulator state in Ta2NiSe5 probed by photoemission spectroscopy, Physi- cal review letters 103, 026402 (2009)

    2009

  7. [14]

    Pillo, J

    T. Pillo, J. Hayoz, H. Berger, F. L´ evy, L. Schlapbach, and P. Aebi, Photoemission of bands above the fermi level: The excitonic insulator phase transition in 1T- TiSe 2, Physical Review B 61, 16213 (2000)

    2000

  8. [15]

    K. Seki, Y. Wakisaka, T. Kaneko, T. Toriyama, T. Kon- ishi, T. Sudayama, N. Saini, M. Arita, H. Namatame, M. Taniguchi, et al. , Excitonic Bose-Einstein condensa- tion in Ta2NiSe5 above room temperature, Physical Re- view B 90, 155116 (2014)

    2014

  9. [16]

    Sugawara, Y

    K. Sugawara, Y. Nakata, R. Shimizu, P. Han, T. Hito- sugi, T. Sato, and T. Takahashi, Unconventional charge- density-wave transition in monolayer 1T-TiSe 2, ACS nano 10, 1341 (2016)

    2016

  10. [17]

    Kogar, M

    A. Kogar, M. S. Rak, S. Vig, A. A. Husain, F. Flicker, Y. I. Joe, L. Venema, G. J. MacDougall, T. C. Chiang, E. Fradkin, et al. , Signatures of exciton condensation in a transition metal dichalcogenide, Science 358, 1314 (2017)

    2017

  11. [18]

    Y. Song, C. Jia, H. Xiong, B. Wang, Z. Jiang, K. Huang, J. Hwang, Z. Li, C. Hwang, Z. Liu, et al. , Signatures of the exciton gas phase and its condensation in monolayer 1T-ZrTe2, Nature communications 14, 1116 (2023)

    2023

  12. [19]

    Gao, Y.-h

    Q. Gao, Y.-h. Chan, Y. Wang, H. Zhang, P. Jinxu, S. Cui, Y. Yang, Z. Liu, D. Shen, Z. Sun,et al., Evidence of high- temperature exciton condensation in a two-dimensional semimetal, Nature Communications 14, 994 (2023)

    2023

  13. [20]

    Gao, Y.-h

    Q. Gao, Y.-h. Chan, P. Jiao, H. Chen, S. Yin, K. Tang- prapha, Y. Yang, X. Li, Z. Liu, D. Shen, et al. , Ob- servation of possible excitonic charge density waves and metal–insulator transitions in atomically thin semimet- als, Nature Physics , 1 (2024)

    2024

  14. [21]

    Y. H. Kwan, T. Devakul, S. Sondhi, and S. Parameswaran, Theory of competing excitonic orders in insulating WTe 2 monolayers, Physical Review B 104, 125133 (2021)

    2021

  15. [22]

    Y. Jia, P. Wang, C.-L. Chiu, Z. Song, G. Yu, B. J¨ ack, S. Lei, S. Klemenz, F. A. Cevallos, M. Onyszczak, et al., Evidence for a monolayer excitonic insulator, Nature Physics 18, 87 (2022)

    2022

  16. [23]

    B. Sun, W. Zhao, T. Palomaki, Z. Fei, E. Runburg, P. Malinowski, X. Huang, J. Cenker, Y.-T. Cui, J.-H. Chu, et al. , Evidence for equilibrium exciton condensa- tion in monolayer WTe2, Nature Physics 18, 94 (2022)

    2022

  17. [24]

    Que, Y.-H

    Y. Que, Y.-H. Chan, J. Jia, A. Das, Z. Tong, Y.-T. Chang, Z. Cui, A. Kumar, G. Singh, S. Mukherjee, et al., A gate-tunable ambipolar quantum phase transition in a topological excitonic insulator, Advanced Materials 36, 2309356 (2024)

    2024

  18. [25]

    Rossnagel, L

    K. Rossnagel, L. Kipp, and M. Skibowski, Charge- density-wave phase transition in 1T-TiSe2: Excitonic in- sulator versus band-type Jahn-Teller mechanism, Physi- cal Review B 65, 235101 (2002)

    2002

  19. [26]

    Porer, U

    M. Porer, U. Leierseder, J.-M. M´ enard, H. Dachraoui, L. Mouchliadis, I. Perakis, U. Heinzmann, J. Demsar, K. Rossnagel, and R. Huber, Non-thermal separation of electronic and structural orders in a persisting charge density wave, Nature materials 13, 857 (2014)

    2014

  20. [27]

    Wegner, J

    A. Wegner, J. Zhao, J. Li, J. Yang, A. Anikin, G. Kara- petrov, K. Esfarjani, D. Louca, and U. Chatterjee, Ev- idence for pseudo–Jahn-Teller distortions in the charge density wave phase of 1T-TiSe2, Physical Review B 101, 195145 (2020)

    2020

  21. [28]

    Jeong, J

    D. Jeong, J. Kim, K.-H. Jin, J. Kim, and H. W. Yeom, Dichotomy of metallic electron density and charge den- sity wave in 1T-TiSe 2, Physical Review B 109, 125117 (2024)

    2024

  22. [29]

    M. D. Watson, I. Markovi´ c, E. A. Morales, P. Le F` evre, M. Merz, A. A. Haghighirad, and P. D. King, Band hy- bridization at the semimetal-semiconductor transition of Ta2NiSe5 enabled by mirror-symmetry breaking, Physi- cal Review Research 2, 013236 (2020)

    2020

  23. [30]

    Windg¨ atter, M

    L. Windg¨ atter, M. R¨ osner, G. Mazza, H. H¨ ubener, A. Georges, A. J. Millis, S. Latini, and A. Rubio, Common Microscopic Origin of The Phase Transitions in Ta 2NiS5 and The Excitonic Insulator Candidate Ta2NiSe5, npj Computational Materials 7, 210 (2021). 5

    2021

  24. [31]

    H. Lu, M. Rossi, J.-h. Kim, H. Yavas, A. Said, A. Nag, M. Garcia-Fernandez, S. Agrestini, K.-J. Zhou, C. Jia, et al. , Evolution of the electronic structure in Ta 2NiSe5 across the structural transition revealed by resonant in- elastic x-ray scattering, Physical Review B 103, ...

    2021

  25. [32]

    Kaneko, T

    T. Kaneko, T. Toriyama, T. Konishi, and Y. Ohta, Orthorhombic-to-monoclinic phase transition of Ta2NiSe5 induced by the Bose-Einstein condensa- tion of excitons, Physical Review B—Condensed Matter and Materials Physics 87, 035121 (2013)

    2013

  26. [33]

    Mazza, M

    G. Mazza, M. R¨ osner, L. Windg¨ atter, S. Latini, H. H¨ ubener, A. J. Millis, A. Rubio, and A. Georges, Nature of symmetry breaking at the excitonic insulator transition: Ta2NiSe5, Physical review letters124, 197601 (2020)

    2020

  27. [34]

    G. D. Scholes and G. Rumbles, Excitons in nanoscale systems, Nature materials 5, 683 (2006)

    2006

  28. [35]

    X. Cui, C. Wang, A. Argondizzo, S. Garrett-Roe, B. Gumhalter, and H. Petek, Transient excitons at metal surfaces, Nature Physics 10, 505 (2014)

    2014

  29. [36]

    Byrnes, N

    T. Byrnes, N. Y. Kim, and Y. Yamamoto, Exciton– polariton condensates, Nature Physics 10, 803 (2014)

    2014

  30. [37]

    Tanimura, K

    H. Tanimura, K. Tanimura, and P. Van Loosdrecht, Dy- namics of incoherent exciton formation in Cu 2O: Time- and angle-resolved photoemission spectroscopy, Physical Review B 100, 115204 (2019)

    2019

  31. [38]

    Mad´ eo, M

    J. Mad´ eo, M. K. Man, C. Sahoo, M. Campbell, V. Pa- reek, E. L. Wong, A. Al-Mahboob, N. S. Chan, A. Kar- makar, B. M. K. Mariserla, et al. , Directly visualizing the momentum-forbidden dark excitons and their dynam- ics in atomically thin semiconductors, Science 370, 1199 (2020)

    2020

  32. [39]

    M. K. Man, J. Mad´ eo, C. Sahoo, K. Xie, M. Campbell, V. Pareek, A. Karmakar, E. L. Wong, A. Al-Mahboob, N. S. Chan, et al. , Experimental measurement of the intrinsic excitonic wave function, Science advances 7, eabg0192 (2021)

    2021

  33. [40]

    Karni, E

    O. Karni, E. Barr´ e, V. Pareek, J. D. Georgaras, M. K. Man, C. Sahoo, D. R. Bacon, X. Zhu, H. B. Ribeiro, A. L. O’Beirne, et al., Structure of the moir´ e exciton captured by imaging its electron and hole, Nature 603, 247 (2022)

    2022

  34. [41]

    R. Mori, S. Ciocys, K. Takasan, P. Ai, K. Currier, T. Mo- rimoto, J. E. Moore, and A. Lanzara, Spin-polarized spa- tially indirect excitons in a topological insulator, Nature 614, 249 (2023)

    2023

  35. [42]

    Pareek, D

    V. Pareek, D. R. Bacon, X. Zhu, Y.-H. Chan, F. Bussolotti, N. S. Chan, J. P. Urquizo, K. Watan- abe, T. Taniguchi, M. K. Man, et al. , (preprint) arXiv:2403.08725, submitted: Mar (2024)

    2024 arXiv

  36. [43]

    Rustagi and A

    A. Rustagi and A. F. Kemper, Photoemission signature of excitons, Physical Review B 97, 235310 (2018)

    2018

  37. [44]

    Fukutani, R

    K. Fukutani, R. Stania, C. Il Kwon, J. S. Kim, K. J. Kong, J. Kim, and H. W. Yeom, Detecting photo- electrons from spontaneously formed excitons, Nature Physics 17, 1024 (2021)

    2021

  38. [45]

    M. S. Hossain, T. A. Cochran, Y.-X. Jiang, S. Zhang, H. Wu, X. Liu, X. Zheng, B. Kim, G. Cheng, Q. Zhang, et al. , (preprint) arXiv:2312.15862, submitted: Dec (2023)

    2023 arXiv

  39. [46]

    Huang, B

    J. Huang, B. Jiang, J. Yao, D. Yan, X. Lei, J. Gao, Z. Guo, F. Jin, Y. Li, Z. Yuan, et al. , Evidence for an excitonic insulator state in Ta 2Pd3Te5, Physical Review X 14, 011046 (2024)

    2024

  40. [48]

    Jiang, J

    B. Jiang, J. Yao, D. Yan, Z. Guo, G. Qu, X. Deng, Y. Huang, H. Ding, Y. Shi, Z. Wang, et al. , Surface doping manipulation of the insulating ground states in Ta2Pd3Te5 and Ta2Ni3Te5, Chinese Physics B (2024)

    2024

  41. [49]

    Zhang, Y

    P. Zhang, Y. Dong, D. Yan, B. Jiang, T. Yang, J. Li, Z. Guo, Y. Huang, Q. Li, Y. Li, et al. , Spontaneous gap opening and potential excitonic states in an ideal dirac semimetal Ta 2Pd3Te5, Physical Review X 14, 011047 (2024)

    2024

  42. [50]

    for detail) show that the exciton photoemission sig- nal remains robust below T c (Fig. 2a). However, the excitonic signal moves systematically to a lower energy (Figs. 2a and 2e) with rising temperature, which is con- sistently lower than the valence band top. Namely, the exc...

    2024

  43. [51]

    [11,43-46,49,51,68]

    See Supplemental Material at http://link.aps.org/ sup- plemental/ for additional data and calulated desults, which includes Refs. [11,43-46,49,51,68]

  44. [52]

    X. Wang, D. Geng, D. Yan, W. Hu, H. Zhang, S. Yue, Z. Sun, S. Kumar, E. F. Schwier, K. Shimada, et al. , Observation of topological edge states in the quantum spin hall insulator Ta 2Pd3Te5, Physical Review B 104, L241408 (2021)

    2021

  45. [53]

    C. Chen, J. Avila, E. Frantzeskakis, A. Levy, and M. C. Asensio, Observation of a two-dimensional liquid of fr¨ ohlich polarons at the bare SrTiO3 surface, Nature communications 6, 8585 (2015)

    2015

  46. [54]

    M. Kang, S. W. Jung, W. J. Shin, Y. Sohn, S. H. Ryu, T. K. Kim, M. Hoesch, and K. S. Kim, Holstein polaron in a valley-degenerate two-dimensional semiconductor, Nature materials 17, 676 (2018)

    2018

  47. [55]

    J. M. Riley, F. Caruso, C. Verdi, L. Duffy, M. D. Watson, L. Bawden, K. Volckaert, G. Van Der Laan, T. Hesjedal, M. Hoesch, et al. , Crossover from lattice to plasmonic polarons of a spin-polarised electron gas in ferromagnetic EuO, Nature Communications 9, 2305 (2018)

    2018

  48. [56]

    Antonius, Y.-H

    G. Antonius, Y.-H. Chan, and S. G. Louie, Polaron spec- tral properties in doped zno and srtio 3 from first princi- ples, Physical Review Research 2, 043296 (2020)

    2020

  49. [57]

    Caruso, P

    F. Caruso, P. Amsalem, J. Ma, A. Aljarb, T. Schultz, M. Zacharias, V. Tung, N. Koch, and C. Draxl, Two- dimensional plasmonic polarons in n-doped monolayer MoS2, Physical Review B 103, 205152 (2021)

    2021

  50. [58]

    L. Kang, X. Du, J. Zhou, X. Gu, Y. Chen, R. Xu, Q. Zhang, S. Sun, Z. Yin, Y. Li, et al. , Band-selective holstein polaron in Luttinger liquid material A 0.3MoO3 (A= K, Rb), Nature Communications 12, 6183 (2021)

    2021

  51. [59]

    A. Wang, Y. Li, G. Yang, D. Yan, Y. Huang, Z. Guo, J. Gao, J. Huang, Q. Zeng, D. Qian, et al., A robust and tunable luttinger liquid in correlated edge of transition- metal second-order topological insulator Ta2Pd3Te5, Na- ture Communications 14, 7647 (2023)

    2023

  52. [60]

    Christiansen, M

    D. Christiansen, M. Selig, E. Malic, R. Ernstorfer, and A. Knorr, Theory of exciton dynamics in time- resolved ARPES: Intra-and intervalley scattering in two- dimensional semiconductors, Physical Review B 100, 205401 (2019)

    2019

  53. [61]

    L. Ni, U. Huynh, A. Cheminal, T. H. Thomas, R. Shiv- anna, T. F. Hinrichsen, S. Ahmad, A. Sadhanala, and A. Rao, Real-time observation of exciton–phonon cou- pling dynamics in self-assembled hybrid perovskite quan- tum wells, ACS nano 11, 10834 (2017)

    2017

  54. [62]

    Y. Lu, H. Kono, T. Larkin, A. Rost, T. Takayama, A. Boris, B. Keimer, and H. Takagi, Zero-gap semicon- ductor to excitonic insulator transition in Ta 2NiSe5, Na- ture communications 8, 14408 (2017). 6

    2017

  55. [63]

    Okazaki, Y

    K. Okazaki, Y. Ogawa, T. Suzuki, T. Yamamoto, T. Someya, S. Michimae, M. Watanabe, Y. Lu, M. No- hara, H. Takagi,et al., Photo-induced semimetallic states realised in electron–hole coupled insulators, Nature com- munications 9, 4322 (2018)

    2018

  56. [64]

    Werdehausen, T

    D. Werdehausen, T. Takayama, G. Albrecht, Y. Lu, H. Takagi, and S. Kaiser, Photo-excited dynamics in the excitonic insulator Ta 2NiSe5, Journal of Physics: Con- densed Matter 30, 305602 (2018)

    2018

  57. [65]

    C. Chen, X. Chen, W. Tang, Z. Li, S. Wang, S. Ding, Z. Kang, C. Jozwiak, A. Bostwick, E. Rotenberg, et al. , Role of electron-phonon coupling in excitonic insulator candidate Ta2NiSe5, Physical Review Research 5, 043089 (2023)

    2023

  58. [66]

    C. Chen, W. Tang, X. Chen, Z. Kang, S. Ding, K. Scott, S. Wang, Z. Li, J. P. Ruff, M. Hashimoto, et al. , Anomalous excitonic phase diagram in band-gap-tuned Ta2Ni(Se, S)5, Nature Communications 14, 7512 (2023)

    2023

  59. [67]

    R. Wang, O. Erten, B. Wang, and D. Xing, Prediction of a topological p+ ip excitonic insulator with parity anomaly, Nature communications 10, 210 (2019)

    2019

  60. [68]

    Kozii and L

    V. Kozii and L. Fu, Odd-parity superconductivity in the vicinity of inversion symmetry breaking in spin-orbit- coupled systems, Physical review letters 115, 207002 (2015)

    2015

  61. [69]

    Z. Guo, D. Yan, H. Sheng, S. Nie, Y. Shi, and Z. Wang, Quantum spin Hall effect in Ta 2M3Te5 (M= Pd, Ni), Physical Review B 103, 115145 (2021)

    2021

  62. [70]

    Y. Li, D. Yan, Y. Hong, H. Sheng, A. Wang, Z. Dou, X. Guo, X. Shi, Z. Su, Z. Lyu, et al. , Interfering joseph- son diode effect in Ta 2Pd3Te5 asymmetric edge interfer- ometer, Nature Communications 15, 9031 (2024)

    2024

  63. [71]

    H. Yu, D. Yan, Z. Guo, Y. Zhou, X. Yang, P. Li, Z. Wang, X. Xiang, J. Li, X. Ma, et al. , Observation of emergent superconductivity in the topological insula- tor Ta2Pd3Te5 via pressure manipulation, Journal of the American Chemical Society 146, 3890 (2024)

    2024

  64. [72]

    Zhang, P

    P. Zhang, P. Richard, T. Qian, Y.-M. Xu, X. Dai, and H. Ding, A precise method for visualizing dispersive fea- tures in image plots, Review of Scientific Instruments 82 (2011)

    2011

  65. [73]

    Kresse and J

    G. Kresse and J. Furthm¨ uller, Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set, Physical review B 54, 11169 (1996)

    1996

  66. [74]

    J. P. Perdew, K. Burke, and M. Ernzerhof, Generalized gradient approximation made simple, Physical review let- ters 77, 3865 (1996)

    1996

  67. [75]

    Exciton photoemission from a ground state of a solid T a2Pd3T e5

    T. Kaneko and Y. Ohta, A new era of excitonic insula- tors, Journal of the Physical Society of Japan 94, 012001 (2025). 7 FIG. 1: a) An experimental setup of exciton photoemission with linearly polarized light. The squared exciton radial wave function simulated with experiment...

    2025

  68. [76]

    At present, we can note that the DFT-optimized structure model reproduces the fine details of the high-resolution STM topographies as shown in Fig

    Electronic Dominance in STM T opography Without Density W aves We have performed STM/STS/DFT studies on the structural details of this system. At present, we can note that the DFT-optimized structure model reproduces the fine details of the high-resolution STM topographies as ...

  69. [77]

    Ta 2Pd3Te5 have three major orbitals that constitute valence and conduction bands

    Polarization dependence of exciton photoemission The polarization dependence in ARPES spectra is di- rectly related to the mirror symmetry of orbitals in the involved bands through the dipole selection rule of an optical transition. Ta 2Pd3Te5 have three major orbitals that co...

  70. [78]

    Fittings of exciton wavefunction We have followed the previous theoretical model and similar experimental assumptions, which were used for the ARPES work on Ta 2NiSe5 [43, 44]. The theoreti- cal model was originally designed for excitons induced by optical pulses in time-resol...

  71. [79]

    The M-shaped band is a trivial valence band that does not contribute to exciton formation

    Two valence bands with different shapes The butterfly-shaped valence bands consist of two dis- tinct components: one exhibiting an M-shaped disper- sion and the other a Λ-shaped dispersion (Figure S7a and S7b). The M-shaped band is a trivial valence band that does not contribu...

  72. [80]

    (D3) σi are the Pauli matrices

    Two band model calculation with an excitonic interaction In order to examine the excitonic correlation properly, we considered the minimal band model (two-band model) with the excitonic interaction term, as follows : H = h(k)σ0 + M (k)σz + Ax sin(kx)σx + Ay sin(ky)σy + hei, (D...

  73. [81]

    The sum of this function with the simulated exciton contribution results in a broad- ened valence band feature (Figure S10f)

    ARPES simulation and electron-phonon interaction To rule out the possibility of electron-phonon cou- pling as the origin of our unusual photoemission feature, we simulated the valence band spectrum using a sim- ple Bethe-Salpeter equation model with two quadratic bands (Figure...

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