On-Chip Terahertz Pump–Probe Spectroscopy Revealing Ultrafast Current-Induced Breakdown Dynamics in a Superconducting Nb Microstrip

On-chip terahertz (THz) spectroscopy has attracted growing attention because of its capability of measuring samples far smaller than the Rayleigh diffraction limit. The technique also allows the investigation of nonlinear responses of materials, which is indispensable for the development of ultrafast devices operating with a THz bandwidth. Here, we report the development of an on-chip THz-pump THz-probe spectroscopy technique that enables the study of ultrafast electrical-pulse-induced nonequilibrium phenomena. Using this setup, we observed ultrafast dynamics of the current-induced superconducting-to-normal state transition in a Nb microstrip. The current density of the picosecond pulse required to destroy the superconducting state far exceeds that of the direct-current supercurrent. The results, including the nonequilibrium dynamics of the superconducting order parameter, were explained by the time-dependent Ginzburg-Landau theory. The developed on-chip THz-pump THz-probe spectroscopy system offers a new platform for the characterization and manipulation of quantum materials integrated into electrical circuits with an ultrafast time resolution.