The quantum conductance of ballistic microconstrictions in metals with an open Fermi surface

It is shown that the conductance $G$ of the quantum microconstriction in the metal with an opened Fermi surface as a function of the contact diameter undergoes the jumps $e^{2}/h$ of the opposite sign. The negative jumps is the result of the limitation of the energy of the electron motion along the direction, in which the Fermi surface is opened. The point contact spectrum $dG/dV$ of such constriction has additional peaks at the bias $eV$ when the maximal energy $\epsilon_{\max}$ of the quantum subband is equal to the energies $\epsilon_{F}\pm \frac{eV}{2}$ ($\epsilon_{F}$ is the Fermi energy).