Influence of nonequilibrium phonons on the energy gap of superconductors

We consider the influence of isotropic phonon pumping at frequency Ω on the magnitude of the energy gap Δ in the spectrum of the quasiparticle excitations of a superconductor. It is shown that close to the superconducting transition temperature Tc, when the frequency is Ω < 2Δ, a strengthening of the superconductivity (an increase in Δ and in Tc) may occur due mainly to the direct influence of the distribution of nonequilibrium (real) phonons on the virtual Cooper pairing process. This mechanism is more effective than the mechanism of stimulated superconductivity of Éliashberg by the parameter [λ (Ω/Tc)(Ω τ ε)]−1 when Ω ≪ 2Δ (where λ is the BCS pairing constant and τε, is the energy relaxation time for the quasiparticles).

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