Momentum-resolved resonant photoelectron spectroscopic study for
1T-TiSe2​: Observation of negative q in the Fano resonance due to
inter-atomic interaction in the valence band
The remarkable properties of (1T-)TiSe2​ among the transition metal
dichalcogenides have attracted the attention of many researchers due to its
peculiar behavior during the charge density wave (CDW) transition. Therefore,
it is highly desirable to study its electronic structure down to the atomic
orbitals. In the present research, we applied momentum-resolved resonant
photoelectron spectroscopy to study TiSe2​ at the Ti2p-Ti3d absorption edge
by using a momentum microscope, which can simultaneously detect the electronic
states in a wide (kx​,ky​) range. We have also used constant initial state
(CIS) spectroscopy and density functional theory (DFT) calculations to reveal
the hybridization between the Ti3d and Se4p orbitals within the valence band at
the Gamma point at room temperature. In addition, an interesting result comes
from our analysis of the CIS spectrum for the energy band located at a binding
energy of 2 eV at the M-point. This band, mainly composed of the Se4p orbital,
exhibited a Fano line profile at the Ti2p edge, with a negative value of the
parameter "q". This is the first clear evidence of the inter-atomic
interaction during the valence band photoelectron emission process. This
behavior differs significantly from the standard resonant photoelectron
emission, which usually involves intra-atomic interactions. It also differs
from the multi-atom resonant photoelectron emission (MARPE) observed in the
core-level photoelectron emission, as we focus on the photoelectron emission
from the valence band in this research