Photoemission of bands above the Fermi level: The excitonic insulator phase transition in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mn>1</mml:mn><mml:mi>T</mml:mi><mml:mo>−</mml:mo><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">TiSe</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Pillo, Th.; Hayoz, J.; Berger, H.; Lévy, F.; Schlapbach, L.; Aebi, Philipp

doi:10.1103/physrevb.61.16213

Cited by 125 publications

(79 citation statements)

References 57 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The small overlap E G =-20 ± 15 meV in the normal phase is consistent with the excitonic insulator scenario, as the exciton binding energy is expected to be close to that value. [5,6]. The position of both band maxima in the occupied states is most probably due to a slight Ti overdoping of our samples [3].…”

Section: Pacs Numbersmentioning

confidence: 92%

“…For the sake of simplicity the description is in terms of the surface BZ highsymmetry pointsΓ andM . The 250 K spectra exhibit the three Se 4p-derived bands atΓ and the Ti 3d-derived band atM widely described in the literature [5,6,7]. The thick dotted lines (white) are fits by equation 1, giving for the topmost 4p band a maximum energy of -20 ± 10 meV, and for the Ti 3d a minimum energy of -40 ± 5 meV.…”

Section: Pacs Numbersmentioning

confidence: 99%

“…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].…”

mentioning

confidence: 99%

See 2 more Smart Citations

Evidence for an Excitonic Insulator Phase in1T−TiSe2

et al. 2007

Self Cite

View full text Add to dashboard Cite

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...

show abstract

Section: Pacs Numbersmentioning

confidence: 92%

Section: Pacs Numbersmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Evidence for an Excitonic Insulator Phase in1T−TiSe2

et al. 2007

Self Cite

View full text Add to dashboard Cite

show abstract

“…The main difference with the basic excitonic insulator phase is that the electron-hole coupling does not shift all the conduction bands, providing states which are unperturbed by the transition and therefore tempering the insulating character of the transition. 15 Among the recent ARPES studies on 1T-TiSe 2 , Pillo et al 16 inferred the existence of a small indirect gap and a conduction band in the unoccupied states and supported the exciton condensate phase scenario. Kidd et al also evidenced a small indirect gap with a conduction band in the unoccupied states.…”

Section: Introductionmentioning

confidence: 99%

Temperature-dependent photoemission on1T-TiSe2: Interpretation within the exciton condensate phase model

et al. 2010

Self Cite

View full text Add to dashboard Cite

The charge-density-wave phase transition of 1T-TiSe 2 is studied by angle-resolved photoemission over a wide temperature range. An important chemical-potential shift which strongly evolves with temperature is evidenced. In the framework of the exciton condensate phase, the detailed temperature dependence of the associated order parameter is extracted. Having a mean-field-like behavior at low temperature, it exhibits a nonzero value above the transition, interpreted as the signature of strong excitonic fluctuations, reminiscent of the pseudogap phase of high-temperature superconductors. Integrated intensity around the Fermi level is found to display a trend similar to the measured resistivity and is discussed within the model.

show abstract

“…A comprehensive theory of this CDW formation is yet to be developed. Two main mechanisms are currently considered, driven either by a JahnTeller distortion [4,11] or an excitonic ground state [2,9,12,13]. The CDW phase has been found to melt upon copper intercalation [5] or when applying pressure [7].…”

mentioning

confidence: 99%

Scanning tunneling microscopy of the charge density wave in1T−TiSe2in the presence of single atom defects

et al. 2015

Self Cite

View full text Add to dashboard Cite

We present a detailed low temperature scanning tunneling microscopy study of the commensurate charge density wave (CDW) in 1T -TiSe2 in the presence of single atom defects. We find no significant modification of the CDW lattice in single crystals with native defects concentrations where some bulk probes already measure substantial reductions in the CDW phase transition signature. Systematic analysis of STM micrographs combined with density functional theory modelling of atomic defect patterns indicate that the observed CDW modulation lies in the Se surface layer. The defect patterns clearly show there are no 2H-polytype inclusions in the CDW phase, as previously found at room temperature [Titov A.N. et al, Phys. Sol. State 53, 1073. They further provide an alternative explanation for the chiral Friedel oscillations recently reported in this compound [J. Ishioka et al., Phys. Rev. B 84, 245125, (2011)].PACS numbers: 68.37. Ef, 71.15.Mb, 74.70.Xa, 73.20.Hb The transition metal dichalcogenide (TMD) 1T -TiSe 2 has kept the scientific community wondering about a number of its striking physical properties for more than four decades [1][2][3][4][5][6][7]. 1T -TiSe 2 is a layered compound consisting of a hexagonal layer of Ti sandwiched between two hexagonal layers of Se to form Se-Ti-Se sandwiches that stack via weak Van-der-Waals (VdW) forces to form a single crystal. The band structure of 1T -TiSe 2 , as determined by angle-resolved photoemission spectroscopy, consists primarily of a Se 4p-valence band at the Γ point and a Ti 3d-conduction band at the L point of the Brillouin zone. But it is still debated whether it is a semiconductor or a semimetal with evidences claimed for both alternatives [6,[8][9][10].Below T CDW ≈ 202K, 1T -TiSe 2 undergoes a second order phase transition into a commensurate charge density wave (CDW). A comprehensive theory of this CDW formation is yet to be developed. Two main mechanisms are currently considered, driven either by a JahnTeller distortion [4,11] or an excitonic ground state [2,9,12,13]. The CDW phase has been found to melt upon copper intercalation [5] or when applying pressure [7]. In both instances, superconductivity develops in a dome shaped region around some optimal doping or optimal pressure, with a maximum critical temperature of 4.1K and 1.8K, respectively. More recently, chiral properties have been reported for the CDW in pristine and copper intercalated 1T -TiSe 2 based on polarized optical reflectometry and scanning tunneling microscopy (STM) [14][15][16].Here we focus on the CDW instability in 1T -TiSe 2 in the presence of native atomic scale defects. Past studies performed using macroscopic probes including resistivity, magnetic susceptibility and optical reflectivity have found atomic intercalation and substitution to be detrimental to the CDW [1,17]. This compound is usually non-stoichiometric with a strong correlation between increasing crystal growth temperature and Ti self-doping leading to the collapse of the CDW phase transition signature in temperature ...

show abstract

Photoemission of bands above the Fermi level: The excitonic insulator phase transition in1T−TiSe2

Cited by 125 publications

References 57 publications

Evidence for an Excitonic Insulator Phase in1T−TiSe2

Evidence for an Excitonic Insulator Phase in1T−TiSe2

Temperature-dependent photoemission on1T-TiSe2: Interpretation within the exciton condensate phase model

Scanning tunneling microscopy of the charge density wave in1T−TiSe2in the presence of single atom defects

Contact Info

Product

Resources

About