  High-resolution angle-resolved photoemission spectroscopy and ultrafast
optical pump-probe spectroscopy were used to study semimetallic 1T - TiTe2
quasiparticle dispersion and dynamics. A kink and a flat band, having the same
energy scale and temperature-dependent behaviors along the G-M direction, were
detected. Both manifested at low temperatures but blurred as temperature
increased. The kink was formed by an electron-phonon coupling. And the
localized flat band might be closely related to an electron-phonon coupling.
Ultrafast optical spectroscopy identified multiple distinct time scales in the
10-300 K range. Quantitative analysis of the fastest decay process evidenced a
significant lifetime temperature dependence at high temperatures, while this
starts to change slowly below ~ 100 K where an anomalous Hall coefficient
occurred. At low temperature, a coherent A1g phonon mode with a frequency of ~
4.36 THz was extracted. Frequency temperature dependence suggests that phonon
hardening occurs as temperature falls and anharmonic effects can explain it.
Frequency fluence dependence indicates that the phonons soften as fluence
increases.
