Employing the Keldysh diagram technique, we calculate the electron-phonon energy relaxation rate in a conductor with the vibrating and static δ-correlated random electron-scattering potentials. If the scattering potential is completely dragged by phonons, this model yields the Schmid’s result for the inelastic electron-scattering rate ${\tau }_{e-\mathrm{ph}}^{-1}.$ At low temperatures the effective interaction decreases due to disorder, and ${\tau }_{e-\mathrm{ph}}^{-1}\propto T^{4}l$ (l is the electron mean-free path). In the presense of the static potential, quantum interference of numerous scattering processes drastically changes the effective electron-phonon interaction. In particular, at low temperatures the interaction increases, and ${\tau }_{e-\mathrm{ph}}^{-1}\propto T^2/l.\mathrm{}$ Along with an enhancement of the interaction, which is observed in disordered metallic films and semiconducting structures at low temperatures, the suggested model allows us to explain the strong sensitivity of the electron relaxation rate to the microscopic quality of a particular film.

This paper reviews the state of rapidly emerging terahertz hot-electron nanobolometers (nano-HEB), which are currently among of the most sensitive radiation power detectors at submillimeter wavelengths. With the achieved noise equivalent power close to 10^-19 W/Hz^1/2 and potentially capable of approaching NEP ~ 10^-20 W/Hz^1/2, nano-HEBs are very important for future space astrophysics platforms with ultralow submillimeter radiation background. The ability of these sensors to detect single low-energy photons with high dynamic range opens interesting possibilities for quantum calorimetry in the midinfrared and even in the far-infrared parts of the electromagnetic spectrum. We discuss the competition in the field of ultrasensitive detectors, the physics and technology of nano-HEBs, recent experimental results, and perspectives for future development.

Inelastic electron scattering at the interface between a conducting film and an insulating substrate provides a new channel for energy transfer from the film electrons to the substrate phonons. Its contribution to the Kapitza conductance is found to be $ħu\gamma {/k}_B{\tau }_{e-\mathrm{ph}},$ where $u$ is the sound velocity, γ is the Sommerfeld constant, and ${\tau }_{e-\mathrm{ph}}$ is the electron-phonon energy relaxation time in the film. This mechanism is significant for conductors with strong electron-phonon coupling, or for an interface with a small value of the phonon transparency. The results of the theory agree in order of magnitude with the observed decrease of the Kapitza conductance at the transition to the superconducting state. They can explain a universal minimal value of the conductance for pairs of materials with rather different acoustic impedances (metallic films on diamond substrate). This scattering mechanism results in the nonequilibrium component of the photoresponse with the ps decay time proportional to the film thickness that has been recently observed in YBaCuO ultrathin films.