Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cross-over from BCS superconductivity to Bose condensation and High-Tc
  Superconductors   We consider the Eliashberg theory in the coupling region where some
fundamental qualitative deviations from the conventional BCS-like behaviour
begin to appear. These deviations are identified as the onset of a cross-over
from BCS superconductivity to Bose condensation. We point out that the
beginning of this cross-over occurs when the gap $\Delta_g$ becomes comparable
to the boson energies $\Omega_{ph}$. This condition is equivalent to the
condition of Ref. \cite{Strinati} $k_F\xi\approx 2\pi$ and traduces the
physical constraint that the distance the paired electron covers during the
absorbtion of the virtual boson, cannot be larger than the coherence length.
The frontier region of couplings is of the order of $\lambda\approx 3$, and
high-$T_c$ materials are concerned. A clear qualitative indication of the
occurence of a cross-over regime should be a dip structure above the gap in the
density of states of excitations. Comparing our results with tunneling and
photoemission experiments we conclude that high-$T_c$ materials (cuprates and
fullerides) are indeed at the beginning of a cross-over from BCS
superconductivity to Bose condensation, even though the fermionic nature still
prevails. Taking into account the analysis of Ref. \cite{Strinati}, we predict
a dip structure in heavy fermion and organic superconductors. Non-adiabatic
effects beyond Migdal's theory are considered and give insight on the
robustness of Eliashberg theory in describing qualitatively this cross-over
regime, although for the quantitative interpretation of the results the
inclusion of non-adiabatic corrections can be important.

6
The categories of this paper are: astro-ph
11
The categories of this paper are: hep-lat
29
The categories of this paper are: funct-an
8
The categories of this paper are: hep-ex
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
16
The categories of this paper are: stat
21
The categories of this paper are: adap-org
5
The categories of this paper are: gr-qc
17
The categories of this paper are: q-fin
9
The categories of this paper are: nlin
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
27
The categories of this paper are: comp-gas