  The critical temperature (${T}_\text{c}$) of superconductors varies a lot.
The factors governing the ${T}_\text{c}$ may hold key clues to understand the
nature of the superconductivity. Thereby, ${T}_\text{c}$-involved correlations,
such as Matthias laws, Uemura law, and cuprates doping phase diagrams, have
been of great concern. However, the electronic interaction being responsible
for the carriers pairing in high-${T}_\text{c}$ superconductors is still not
clear, which calls for more comprehensive analyses of the experimental data in
history. In this work, we propose a novel perspective for searching material
gene parameters and ${T}_\text{c}$-involved correlations. By exploring holistic
band structure features of diverse superconductors, we found a universal
correlation between the ${T}_\text{c}$ maxima and the electron energy levels
for all kinds of superconducting materials. It suggests that the ${T}_\text{c}$
maxima are determined by the energy level of secondary-outer orbitals, rather
than the band structure nearby the Fermi level. The energy level of
secondary-outer orbitals is a parameter corresponding to the ratio of atomic
orbital hybridization, implying that the fluctuation of the orbital
hybridization is another candidate of pairing glue.
