X-Ray Studies of Phonon Softening in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>TiSe</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Holt, Martin V.; Zschack, P.; Hong, Hawoong; Chou, M. Y.; Chiang, T.‐C.

doi:10.1103/physrevlett.86.3799

Cited by 153 publications

(145 citation statements)

References 16 publications

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“…In fact, it is the value estimated by Holt et al at T ≃ 150K for the transverse phonon mode, which softens at L at the transition [31]. This corresponds to a situation where the ionic displacement u lµ is not too large, such that our first order development of the electron-phonon coupling remains valid.…”

Section: Transfer Integralmentioning

confidence: 75%

Exciton Condensation Driving the Periodic Lattice Distortion of1T−TiSe2

et al. 2011

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We address the lattice instability of 1T -TiSe2 in the framework of the exciton condensate phase. We show that, at low temperature, condensed excitons influence the lattice through electron-phonon interaction. It is found that at zero temperature, in the exciton condensate phase of 1T -TiSe2, this exciton condensate exerts a force on the lattice generating ionic displacements comparable in amplitude to what is measured in experiment. This is thus the first quantitative estimation of the amplitude of the periodic lattice distortion observed in 1T -TiSe2 as a consequence of the exciton condensate phase.

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Section: Transfer Integralmentioning

confidence: 75%

Exciton Condensation Driving the Periodic Lattice Distortion of1T−TiSe2

et al. 2011

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“…The parallels with several families of materials where the superconducting dome has been discovered in the vicinity of purely electronic ordered phase, dressing the quantum critical point [16][17][18] strengthen the viewpoint of excitonic superconductivity in 1T-TiSe 2 . On the other hand, the continuous development of the soft phonon mode in the vicinity of the CDW transition, both in Cu-intercalated and pure and pressurized material [8,34,35], suggests that the lattice deformation may not be regarded as a secondary effect that simply follows the electronic ordering. The soft phonon mode, generally regarded as unfavorable for superconductivity within the weak-coupling BCS single-phonon exchange picture, has been identified as helpful in several instances for higher values of the electron-phonon coupling [36][37][38][39].…”

Section: Fig 1 (Color Online)mentioning

confidence: 99%

Pressure Induced Superconductivity in Pristine1T−TiSe2

et al. 2009

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“…One of the most frequent characteristics is a ground state exhibiting a charge-density wave (CDW), with its origin arising from a particular topology of the Fermi surface and/or a strong electron-phonon coupling [2]. Among the TMDC's 1T -TiSe 2 shows a commensurate 2×2×2 structural distortion below 202 K, accompanied by the softening of a zone boundary phonon and with changes in the transport properties [3,4]. In spite of many experimental and theoretical studies, the driving force for the transition remains controversial.…”

Section: Pacs Numbersmentioning

confidence: 99%

Evidence for an Excitonic Insulator Phase in1T−TiSe2

et al. 2007

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We present a new high-resolution angle-resolved photoemission study of 1T -TiSe2 in both, its room-temperature, normal phase and its low-temperature, charge-density wave phase. At low temperature the photoemission spectra are strongly modified, with large band renormalisations at highsymmetry points of the Brillouin zone and a very large transfer of spectral weight to backfolded bands. A theoretical calculation of the spectral function for an excitonic insulator phase reproduces the experimental features with very good agreement. This gives strong evidence in favour of the excitonic insulator scenario as a driving force for the charge-density wave transition in 1T -TiSe2. PACS numbers:Transition-metal dichalcogenides (TMDC's) are layered compounds exhibiting a variety of interesting physical properties, mainly due to their reduced dimensionality [1]. One of the most frequent characteristics is a ground state exhibiting a charge-density wave (CDW), with its origin arising from a particular topology of the Fermi surface and/or a strong electron-phonon coupling [2]. Among the TMDC's 1T -TiSe 2 shows a commensurate 2×2×2 structural distortion below 202 K, accompanied by the softening of a zone boundary phonon and with changes in the transport properties [3,4]. In spite of many experimental and theoretical studies, the driving force for the transition remains controversial. Several angle-resolved photoelectron spectroscopy (ARPES) studies suggested either the onset of an excitonic insulator phase [5,6] or a band Jahn-Teller effect [7]. Furthermore, TiSe 2 has recently attracted strong interest due to the observation of superconductivity when intercalated with Cu [8]. In systems showing exotic properties, such as Kondo systems for example [9], the calculation of the spectral function has often been a necessary and decisive step for the interpretation of the ARPES data and the determination of the ground state of the systems. In the case of 1T -TiSe 2 , such a calculation for an excitonic insulator phase lacked so far.In this letter we present a high-resolution ARPES study of 1T -TiSe 2 , together with theoretical calculations of the excitonic insulator phase spectral function for this compound. We find that the experimental ARPES spectra show strong band renormalisations with a very large transfer of spectral weight into backfolded bands in the low-temperature phase. The spectral function calculated for the excitonic insulator phase is in strikingly good * Electronic address: herve.cercellier@unine.ch agreement with the experiments, giving strong evidence for the excitonic origin of the transition.The excitonic insulator model was first introduced in the sixties, for a semi-conductor or a semi-metal with a very small indirect gap E G [10,11,12,13]. Thermal excitations lead to the formation of holes in the valence band and electrons in the conduction band. For low free carrier densities, the weak screening of the electronhole Coulomb interaction leads to the formation of stable electron-hole bound states, called excito...

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X-Ray Studies of Phonon Softening inTiSe2

Cited by 153 publications

References 16 publications

Exciton Condensation Driving the Periodic Lattice Distortion of1T−TiSe2

Exciton Condensation Driving the Periodic Lattice Distortion of1T−TiSe2

Pressure Induced Superconductivity in Pristine1T−TiSe2

Evidence for an Excitonic Insulator Phase in1T−TiSe2

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