Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Non-Coulomb strong electron-hole binding in $Ta_2NiSe_5$ revealed by
  time- and angle-resolved photoemission spectroscopy   We reveal an ultrafast purely electronic phase transition in \TNS, which is a
plausible excitonic insulator, after excited by an ultrafast infrared laser
pulse. Specifically, the order parameter of the strong electron-hole binding
shrinks with enhancing the pump pulse, and above a critical pump fluence, a
photo-excited semimetallic state is experimentally identified with the absence
of ultrafast structural transition. In addition, the bare valence and
conduction bands and also the effective exciton binding energy in \TNS~are
determined. These findings and detailed analysis suggest a bare nonequilibrium
semimetallic phase in $Ta_2NiSe_5$ and the strong electron-hole binding cannot
be exclusively driven by Coulomb interaction.

15
The categories of this paper are: nucl-ex
37
The categories of this paper are: supr-con
3
The categories of this paper are: physics
23
The categories of this paper are: solv-int
30
The categories of this paper are: q-alg
19
The categories of this paper are: eess
18
The categories of this paper are: econ
2
The categories of this paper are: math
17
The categories of this paper are: q-fin
22
The categories of this paper are: chao-dyn
25
The categories of this paper are: patt-sol
20
The categories of this paper are: acc-phys
33
The categories of this paper are: plasm-ph
26
The categories of this paper are: bayes-an
9
The categories of this paper are: nlin
1
The categories of this paper are: cs