Reabsorption of nonequilibrium phonons at superconducting point contacts
  When there is a deviation from the inequality $d\ll {{l}_{\varepsilon }}$ ($d$ is the contact diameter, and ${{l}_{\varepsilon }}$ is the energy relaxation length of the electrons), structural features are produced on the current-voltage characteristics of $S-c-N$ contacts at characteristic phonon energies because of the decrease in $\Delta $ due to the accumulation of nonequilibrium phonons with low group velocities near the contact. 
I. K. Yanson, V. V. Fisun, N. L. Bobrov, and L. F. Rybal'chenko
cond-mat.supr-con