Microjunction spectroscopy of the populations of two-level systems

Consideration is given to the nonlinear contribution of a metallic microjunction to the volt-ampere characteristics caused by the scattering of electrons by low-energy excitations (two-level systems). The possibility of a novel type of microjunction spectroscopy is demonstrated; i.e., the population spectroscopy of two-level systems due to the dependence of the occupation numbers of a two-level system on the voltage at the junction. The shape of the microjunction spectral line is asymmetrical and consists of a central peak at a value of eV equal to the excitation energy and a wing at energies exceeding the latter value. The nonlinear component of the conductivity exhibits a strong frequency dispersion at frequencies of 10 to the 3rd to 10 to the 9th Hz due to the relaxation of the two-level excitations which may serve as a distinguishing feature of the present scattering mechanism.