3 research outputs found
A versatile laser-based apparatus for time-resolved ARPES with micro-scale spatial resolution
We present the development of a versatile apparatus for a 6.2 eV laser-based
time and angle-resolved photoemission spectroscopy with micrometer spatial
resolution (time-resolved -ARPES). With a combination of tunable spatial
resolution down to 11 m, high energy resolution (11 meV),
near-transform-limited temporal resolution (280 fs), and tunable 1.55 eV
pump fluence up to 3 mJ/cm, this time-resolved -ARPES system
enables the measurement of ultrafast electron dynamics in exfoliated and
inhomogeneous materials. We demonstrate the performance of our system by
correlating the spectral broadening of the topological surface state of
BiSe with the spatial dimension of the probe pulse, as well as
resolving the spatial inhomogeneity contribution to the observed spectral
broadening. Finally, after in-situ exfoliation, we performed time-resolved
-ARPES on a 30 m few-layer-thick flake of transition metal
dichalcogenide WTe, thus demonstrating the ability to access ultrafast
electron dynamics with momentum resolution on micro-exfoliated and twisted
materials
Unveiling the underlying interactions in Ta2NiSe5 from photo-induced lifetime change
We present a generic procedure for quantifying the interplay of electronic
and lattice degrees of freedom in photo-doped insulators through a comparative
analysis of theoretical many-body simulations and time- and angle-resolved
photoemission spectroscopy (TR-ARPES) of the transient response of the
candidate excitonic insulator Ta2NiSe5. Our analysis demonstrates that the
electron-electron interactions dominate the electron-phonon ones. In
particular, a detailed analysis of the TRARPES spectrum enables a clear
separation of the dominant broadening (electronic lifetime) effects from the
much smaller bandgap renormalization. Theoretical calculations show that the
observed strong spectral broadening arises from the electronic scattering of
the photo-excited particle-hole pairs and cannot be accounted for in a model in
which electron-phonon interactions are dominant. We demonstrate that the
magnitude of the weaker subdominant bandgap renormalization sensitively depends
on the distance from the semiconductor/semimetal transition in the
high-temperature state, which could explain apparent contradictions between
various TR-ARPES experiments. The analysis presented here indicates that
electron-electron interactions play a vital role (although not necessarily the
sole one) in stabilizing the insulating state