Tracing the dynamics of superconducting order via transient terahertz third-harmonic generation
Min-Jae Kim, Sergey Kovalev, Mattia Udina, Rafael Haenel, Gideok Kim, Matteo Puviani, Georg Cristiani, Igor Ilyakov, Thales V. A. G. de Oliveira, Alexey Ponomaryov, Jan‐Christoph Deinert, Г. Логвенов, B. Keimer, Dirk Manske, Lara Benfatto, S. Kaiser
Abstract
Ultrafast optical control of quantum systems is an emerging field of physics. In particular, the possibility of light-driven superconductivity has attracted much of attention. To identify nonequilibrium superconductivity, it is necessary to measure fingerprints of superconductivity on ultrafast timescales. Recently, nonlinear THz third-harmonic generation (THG) was shown to directly probe the collective degrees of freedoms of the superconducting condensate, including the Higgs mode. Here, we extend this idea to light-driven nonequilibrium states in superconducting La 2- x Sr x CuO 4 , establishing an optical pump–THz–THG drive protocol to access the transient superconducting order-parameter quench and recovering on few-picosecond timescales. We show in particular the ability of two-dimensional TH spectroscopy to disentangle the effects of optically excited quasiparticles from the pure order-parameter dynamics, which are unavoidably mixed in the pump-driven linear THz response. Benchmarking the gap dynamics to existing experiments shows the ability of driven THG spectroscopy to overcome these limitations in ordinary pump-probe protocols.