Visible/Multi-terahertz 2-Dimensional Spectroscopy of Ultrafast Carrier Dynamics in Quantum Materials

Ultrafast dynamics observed at low energies carry insightful information about the complex many-body interactions in solid-state materials. Here, we present a highly sensitive and robust setup for asymmetric 2-dimensional spectroscopy performing 2-pulse visible excitation combined with probing in the 15- to 35-THz frequency range. This experimental setup is ideal for targeting the interplay of high- and low-energy correlations in functional materials with femtosecond temporal and millielectronvolt energy resolution. In addition, the sub-cycle field resolution of mid-infrared pulses enables tracking nonthermal interactions in the complex dielectric function. Prototypical measurements benchmark ultrafast carrier dynamics in thin-film graphite, showing in detail the interplay of direct and indirect optical transitions in the transient excited state. We further investigate the photo-induced collapse of the superconducting condensate in the high-temperature superconductor Bi 2 Sr 2 CaCu 2 O 8+ x at energies resonant to the optical bandgap, revealing a nontrivial instantaneous nonlinearity related to the excited quasiparticles in the material. Optical pump–terahertz probe experiments build the foundation for this evolutionary step in 2-dimensional spectroscopy as well as for terahertz 4-wave mixing with resonant driving and readout of the superconducting state. Our results offer exciting perspectives in the study of strong correlations and enable precise investigations of nontrivial many-body interactions in few-layer samples and nanostructures.