Attractive Coulomb interaction, temperature-dependent hybridization, and natural circular dichroism in 1T−TiSe2

Abstract

We study the electronic structure of single crystal 1T-TiSe 2 using temperature (T)-dependent soft x-ray photoemission spectroscopy (PES) and natural circular dichroism (NCD) across the charge-density-wave (CDW) transition at T cdw ∼ 200 K. We investigate detailed changes in energy positions and widths of the Ti 2p and Se 3d core-level spectra across T cdw. The Ti 2p-3d-resonant PES shows a clear Ti 3d character two-hole correlation satellite in the valence band. A Cini-Sawatzky analysis indicates an effective attractive two-hole Coulomb interaction energy U dd =−1.3 eV. This attractive Coulomb energy is significantly larger than the known energy scale of excitonic correlations (< 100 meV) in 1T-TiSe 2. On-resonant T-dependent measurements indicate that the strongly hybridized Ti 3d-Se 4p bands show increased hybridization in the CDW phase. On-resonant valence band spectra show a finite, possibly experimental geometry-related NCD of the states at and near the Fermi level which do not show T dependence across T cdw. Given the presence of excitonic effects and the periodic lattice distortion, our results suggest that theoretical models need to take into account the attractive Coulomb interaction and hybridization changes for a complete understanding of the CDW in 1T-TiSe 2 .

Charge-density-wave melted superconductivity in 1T-TiSe2

“…A small but finite doping-dependent change between these two samples is observed, where the inset illustrates the leading edge of the K-edge main peak in an expanded scale. The leading edge of the K-edge main peak shifts to higher photon energy by ∼100 meV for the spectrum of x = 0.25 compared to that of x = 0, indicating the rising of the chemical potential [35].…”

Momentum-Resolved Electronic Structures and Strong Electronic Correlations in Graphene-like Nitride Superconductors

“…Finally, we estimate the value of U experimentally. It is noteworthy that the values of U in Cr metal, Fe metal, K 2 Cr 8 O 16 , TiSe 2 , and CrN compounds have been successfully extracted by soft X-ray resonant photoemission (resonant PES). Figure a shows the incident photon energy ( h ν)-dependent resonant PES spectra of the TiN film.…”

“…However, with a further increase in the incident photon energy from 456 to 466 eV, the two Auger peaks (Ti L 3 VV and L 2 VV) become dominant and have strong dependences on the incident photon energy (see Figure a,c). The values of U (6.26 ± 0.04 eV, see the SI for details) for TiN films can be extracted by the formula U = { E 2p – ( h ν – E LVV )} – 2ε 3d , − where E 2p is the binding energy (BE) of the Ti 2p 3/2 electron (455 eV, see Figure S7 in the SI), h ν is the incident photon energy varied from 456 to 466 eV, and E LVV is the BE of the corresponding L 3VV Auger peaks. The parameter 2ε 3d is the average energy of two uncorrelated holes, which can be obtained from the self-convolution of the single-electron Ti 3d state.…”