Electron–hole instability in 1T-TiSe2 (original) (raw)
Related papers
Electron-Phonon Coupling and the Soft Phonon Mode in TiSe_{2}
Physical Review Letters, 2011
We report high-resolution inelastic x-ray measurements of the soft phonon mode in the chargedensity-wave compound TiSe2. We observe a complete softening of a transverse optic phonon at the L point, i.e. q = (0.5, 0, 0.5), at T ≈ TCDW . Renormalized phonon energies are observed over a large wavevector range (0.3, 0, 0.5) ≤ q ≤ (0.5, 0, 0.5). Detailed ab-initio calculations for the electronic and lattice dynamical properties of TiSe2 are in quantitative agreement with experimental frequencies for the phonon branch involving the soft mode. The observed broad range of renormalized phonon frequencies is directly related to a broad peak in the electronic susceptibility stabilizing the chargedensity-wave ordered state. Our analysis demonstrates that a conventional electron-phonon coupling mechanism can explain a structural instability and the charge-density-wave order in TiSe2 although other mechanisms might further boost the transition temperature.
2010
The charge density wave phase transition of 1T-TiSe2 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 behaviour at low temperature, it exhibits a non-zero value above the transition, interpreted as the signature of strong excitonic fluctuations, reminiscent of the pseudo-gap 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.
The influence of different growth conditions on the charge density wave transition of 1T-TiSe2
Journal of Electron Spectroscopy and Related Phenomena, 2011
To get insight into the influence of different growth conditions of 1T-TiSe 2 onto its charge density wave (CDW) phase transition, we have performed angle-resolved photoelectron spectroscopy (ARPES) on TiSe 2 in its CDW phase at low temperatures comparing the results with resistivity measurements. Though the local resistivity maxima become less pronounced with increasing growth temperatures, we do not find this trend in ARPES. While shape and intensity of the emission near E F change drastically, the backfolded valence bands are not affected. The question of the significance of the peaking resistivity as a characteristical 'fingerprint' of the CDW phase transition arises.
Charge-Density-Wave Phase of 1T-TiSe_{2}: The Influence of Conduction Band Population
Physical Review Letters, 2011
The charge-density wave (CDW) phase of TiSe2 was studied by angle-resolved photoelectron spectroscopy (ARPES) and resistivity measurements investigating the influence of the band gap size and of a varying population of the conduction band. A gradual suppression of the CDW-induced electronic superstructure is observed for a variation of the band gap in the ternary compounds TiCxSe2−x with C=(S, Te) as well as for an occupation of only the conduction band by H2O adsorption-induced band bending. These observations point to an optimum band gap and support an excitonic driving force for the CDW.
Perturbation of charge density waves in 1T−TiSe2
Physical Review B, 2021
In this study, using low-temperature scanning tunneling microscopy (STM), we focus on understanding the native defects in pristine 1T -TiSe2 at the atomic scale. We probe how they perturb the charge density waves (CDWs) and lead to local CDW modulated region formation. These defects influence the correlation length of CDWs. We establish a connection between suppression of CDWs, Ti intercalation, and show how this supports the exciton condensation model of CDW formation in 1T -TiSe2.
Evidence for an Excitonic Insulator Phase in 1T-TiSe_ {2}
2007
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.
Splitting of the Ti-3d bands of TiSe2 in the charge-density wave phase
Applied Surface Science, 2017
Very high resolution angular resolved photoemission (ARPES) spectra on TiSe 2 in two distinct polarization geometries (vertical and horizontal) at temperatures between 300 K and 22 K enabled the observation of details of bands near the Fermi level not reported so far. Calculations of the electronic band structure based on density functional theory (DFT) using B3LYP hybrid functional and MBJ potential (with and without spin-orbit coupling) were performed to obtain the orbital symmetry and dispersion. Two degenerate conduction bands (CB's) were observed at the-point, a weak CB-emission at the A-point, and two non degenerate CB's (i.e. splitting of CB) at the M/L-point of the Brillouin Zone (BZ). The splitting was detected at L for both polarizations, while at M remarkably only for horizontal polarization. These results cannot be fully accounted for by current theories for the charge density wave (CDW) and point to a reduced symmetry of the electronic states, possibly due to the chiral CDW.