The search of the phonon structure at the above-gap energies was carried out for $d^{ 2}V/dI^{ 2}(V)$ spectra of MgB$_{ 2}$ point contacts with a normal metal. The two-band model is assumed not only for the gap structure in $dV/dI(V)$-characteristics, but also for phonons in $d^{ 2}V/dI^{ 2}(V)$ point-contact spectra, with up to the maximum lattice vibration energy. Since the current is carried mostly by charges of 3D-band, whereas the strong electron-phonon interaction occurs in 2D-band, we observe the phonon peculiarities due to ''proximity'' effect in { \it k}-space, which depends on the variation of interband coupling through the elastic scattering.
Categories: cond-mat.supr-con