Rate of electron-phonon relaxation in Niobium

Abstract

Niobium is an important superconducting metal for the fabrication of Josephson junctions and other superconducting devices. One of the parameters which governs the ultimate switching speed of a Josephson junction is the electron-phonon relaxation time. Using ultrafast laser excitation on the Josephson junction1,2, the transition from superconducting to normal and back to superconducting state is monitored by the transient change in voltage across the junction1,2. The rise time of the transient change of voltage is mainly governed by the electron-phonon relaxation time which is ultrafast and cannot be resolved by voltage measurement. In this talk, the electron-phonon relaxation time and electron-phonon coupling constant of niobium was measured by a time resolved thermal modulation3-5 optical transmission technique.