Electrical fluctuations in normal metal point-contacts

The low-frequency electrical fluctuations are measured for point-contacts of Cu, Ag, and Au, the contact diameter being less than the electron mean free path. The $\text{1}\text{?}$ spectral density and a nonmonotonic (oscillating) dependence of r.m.s. noise voltage, V_N, on the d.c. bias, eV, are found. The positions of minima in the V_N(eV) curves are in certain connection with the characteristic phonon energies of metals studied. The phenomenon is attributed to the coherent phonon emission by hot electrons moving along the contact axis.