Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Direct observation of electron thermalization and electron-phonon
  coupling in photoexcited bismuth   We investigate the ultrafast response of the bismuth (111) surface by means
of time resolved photoemission spectroscopy. The direct visualization of the
electronic structure allows us to gain insights on electron-electron and
electron-phonon interaction. Concerning electron-electron interaction, it is
found that electron thermalization is fluence dependent and can take as much as
several hundreds of femtoseconds at low fluences. This behavior is in
qualitative agreement with Landau's theory of Fermi liquids but the data show
deviations from the behavior of a common 3D degenerate electron gas. Concerning
electron-phonon interaction, our data allows us to directly observe the
coupling of individual Bloch state to the coherent $A_{1g}$ mode. It is found
that surface states are much less coupled to this mode when compared to bulk
states. This is confirmed by \textit{ab initio} calculations of surface and
bulk bismuth.

7
The categories of this paper are: hep-th
6
The categories of this paper are: astro-ph
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
35
The categories of this paper are: mtrl-th
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
27
The categories of this paper are: comp-gas
11
The categories of this paper are: hep-lat
3
The categories of this paper are: physics
15
The categories of this paper are: nucl-ex
28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph