Laser thermal point-contact spectroscopy of metals
Abstract
The response of copper spear–thin film (σ ∼ l μm) point contacts to optical laser radiation (λ = 0.63 μm) is studied at helium temperatures. The point contacts are irradiated both from the spear and the film sides. In the latter case, the contact is influenced by the flow of nonequilibrium thermal phonons generated in the film by the incident light. In both cases, the dependence of the response on a fixed bias voltage is essentially identical to the point-contact spectrum of electron–phonon interaction in copper. The signal amplitude is found to depend significantly on the heat transfer conditions. The obtained experimental data suggest that the observed effect is of the thermal origin. This is supported by the theoretical results. The thermal response of the point contact is analyzed theoretically and the basic concepts of laser thermal spectroscopy are formulated. Data for point contacts with nonballistic current flow modes are also reported.