Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Why does maximum Tc occur at the cross-over from weak to strong
  electron-phonon coupling in high temperature superconductors?   In cuprate superconductors, a pronounced maximum of superconducting Tc is
observed in compounds that have an in-plane Cu-O distance close to ~1.92
Angstroms. On the other hand, direct measurements of the electron-phonon
coupling lambda as a function of Cu-O distance show a clear linear correlation,
implying that Tc is a strongly non-linear function of lambda. Conventional
superconductivity theories based on the electron-phonon interaction predict a
monotonic dependence of Tc on electron phonon coupling constant, which makes
them incompatible with the observed behaviour. The observed cross-over
behaviour as a function of lambda suggests that Tc occurs at the cross-over
from weak to strong coupling, which is also associated with the onset of
carrier localization. A coexistence, with a dynamical exchange of localized and
itinerant carriers in a two-component superconductivity scenario are in
agreement with the observed anomalous behavior and are suggested to be the key
to understanding the mechanism for achieving high Tc.

18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio
12
The categories of this paper are: nucl-th
28
The categories of this paper are: alg-geom
7
The categories of this paper are: hep-th
13
The categories of this paper are: quant-ph
16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
11
The categories of this paper are: hep-lat
34
The categories of this paper are: chem-ph
17
The categories of this paper are: q-fin
15
The categories of this paper are: nucl-ex
23
The categories of this paper are: solv-int
27
The categories of this paper are: comp-gas