Nonequilibrium Electric Current-induced Phonon Distribution in Microscale Metallic Structures

The downscaling of modern electronic circuits places an increasing demand on the efficiency of heat dissipation. Electric current-induced heating is generally described in terms of Joule heating – an increase of phonon temperature due to the scattering of electrons on impurities and phonons. We experimentally demonstrate that this interpretation is not universally applicable to microscopic metallic structures. We study the current-dependent resistance R(I) in Pt nanowires. For a 7 μm-long nanowire, we observe a parabolic dependence R(I) at all temperatures T=5 K – 295 K, consistent with the Joule heating. A 1 μm-long nanowire exhibits a similar dependence at T=295 K. In contrast, we observe a singular piecewise-linear dependence at 5 K. As consequence, current-induced resistance increase is much larger than expected from Joule heating at small I, but smaller at large I. The linear dependence persists at modestly increased temperatures, but the singularity becomes broadened, reminiscent of common spectroscopic effects. Our observations are consistent with the non-thermal phonon distribution produced by electron scattering on impurities. The demonstrated effects provide an approach to characterizing and controlling thermal energy dissipation mechanisms.