Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Superconductivity in two-band system with low carrier density   This article is a review o over theory of superconductivity, which is
constructed for systems with two overlapping energy bands at the Fermi surface
and with arbitrary charge carrier density.There is taken into account all
possible kinds of electron pairing within each band and of electron pairing
from different bands. A bell-shape dependence of superconducting-transition
temperature $T_c$ on the electron density, and have demonstrated a possible
onset of HTSC. The absolute and relative jumps of the electron heat capacity
$(C_S - C_N)$ and $(C_S - C_N) / C_N$ at the point $T = T_c$ have been
calculated and the density dependence of these quantities have been
demonstrated. The theory yields both small values $(C_S - C_N) / C_N < 1,43$
and large ones $(C_S - C_N) / C_N > 1,43$. Favorable conditions have been
manifested for an experimental observation of a bend on the chemical-potential
plot $\mu (T)$ at point $T = T_c$ in oxide ceramics and magnezium borid.
  An application of the path integral method to the two-band model is developed
and on this basis, the process of transition from the Fermi to the Bose pattern
of elementary excitations at $T \not = 0$ in the presence of a two-particle
bound state in the system is demonstrated.
  The overlapping of the energy bands on the Fermi surface intensify some
peculiarities of thermodynamic properties at low carrier density. This helps to
their experimental confirmation.

8
The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
21
The categories of this paper are: adap-org
10
The categories of this paper are: q-bio
24
The categories of this paper are: dg-ga
2
The categories of this paper are: math
11
The categories of this paper are: hep-lat
20
The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
25
The categories of this paper are: patt-sol
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
1
The categories of this paper are: cs
31
The categories of this paper are: ao-sci