Evidence of the disorder-independent electron-phonon scattering time in thin NbN films
A.I. Lomakin, E. M. Baeva, A. D. Triznova, N. A. Titova, Philipp Zolotov, A. Semenov, D. E. Sunegin, А. В. Лубенченко, A. I. Kolbatova, Gregory Goltsman
Abstract
We report on experimental study of the effect of disorder on electronic parameters and inelastic scattering mechanisms in ultrathin superconducting NbN films, which are commonly used in single-photon detectors. An increase in disorder in the studied 2.5-nm-thick NbN films characterized by Ioffe-Regel parameter from 6.3 to 1.6 is accompanied by a decrease in the critical temperature ${T}_{c}$ from 11.5 to 3.4 K. By measuring magnetoconductance in the range from ${T}_{c}$ to $\ensuremath{\sim}3{T}_{c}$, we extract the inelastic scattering rates of electrons, including electron-phonon (e-ph) scattering rate ${\ensuremath{\tau}}_{\text{e-ph}}^{\ensuremath{-}1}$. We observe that ${\ensuremath{\tau}}_{\text{e-ph}}^{\ensuremath{-}1}$ and their temperature dependencies are insensitive to disorder that is not described by the existing models of the e-ph scattering in disordered metals. As temperature decreases, the temperature dependence of ${\ensuremath{\tau}}_{\text{e-ph}}^{\ensuremath{-}1}$ varies from ${T}^{3}$ to ${T}^{2}$, which can be result of a decrease in the dimensionality of phonons involved in the e-ph scattering process. Our results call for further theoretical and experimental studies of the e-ph scattering in ultrathin disordered films.