Phonon structure in I-V characteristic of MgB2 point contacts

A search of the phonon structure at the above-gap energies was carried out for d(2)V/dI(2)(V) spectra of MgB2 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 the three-dimensional (3D) band (pi band), whereas the strong electron-phonon interaction occurs in 2D band (sigma band), we observe the phonon peculiarities due to the proximity effect in k space, which depends on both the contact orientation with respect to the crystal axes and the variation of interband coupling through the elastic scattering.