Common behavior of the scaled condensation energy for both high-T_c and conventional superconductors

We analyze the scaling of the condensation energy E_Δ divided by γ, E_Δ/γ≃ N(0)Δ_1^2/γ, of both conventional superconductors and unconventional high-T_c one, where N(0) is the density of states, Δ_1 is the maximum value of the superconducting gap and γ is the Sommerfeld coefficient. For the first time, we show that the universal scaling of E_Δ/γ∝ T_c^2 applies equally to conventional superconductors and unconventional high-T_c ones. Our consideration is based on both facts: Bogoliubov quasiparticles act in conventional and unconventional superconductors, and the corresponding flat band is deformed by the unconventional superconducting state. As a result, our theoretical observations based on the fermion condensation theory are in good agreement with experimental facts.