Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An energy gap in the spectrum of atomic excitations systems   It is shown that atoms in the system can be treated as quantum particles
localized in potential wells, created by atomic potentials of neighboring
atoms. As a result, the state of atoms in the liquid is characterized by wave
functions and the discrete energy spectrum resulting in formation of s and p -
zones corresponding to the ground and excited states of helium atoms,
respectively, separated by a gap. The width of the gap in system equals ~8.5 K
at T=0. Formation of the gap in the energy spectrum of atomic excitations in
helium systems allows us to draw the analogy between the physical mechanisms of
superfluidity and classical superconductivity.

37
The categories of this paper are: supr-con
5
The categories of this paper are: gr-qc
19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
18
The categories of this paper are: econ
24
The categories of this paper are: dg-ga
27
The categories of this paper are: comp-gas
17
The categories of this paper are: q-fin
3
The categories of this paper are: physics
23
The categories of this paper are: solv-int
12
The categories of this paper are: nucl-th
21
The categories of this paper are: adap-org
10
The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat
2
The categories of this paper are: math
13
The categories of this paper are: quant-ph