CC BY 4.0 UnportedWoerner, MichaelGhalgaoui, AhmedReimann, KlausElsaesser, Thomas2022-03-072022-03-072021https://oa.tib.eu/renate/handle/123456789/8182https://doi.org/10.34657/7221Nonlinear two-dimensional terahertz (2D-THz) spectroscopy at frequencies of the emitted THz signal different from the driving frequencies allows for exploring the regime of (off-)resonant even-order nonlinearities in condensed matter. To demonstrate the potential of this method, we study two phenomena in the nonlinear THz response of bulk GaAs: (i) The nonlinear THz response to a pair of femtosecond near-infrared pulses unravels novel fourth- and sixth-order contributions involving interband shift currents, Raman-like excitations of transverse-optical phonon and intervalence-band coherences. (ii) Transient interband tunneling of electrons driven by ultrashort mid-infrared pulses can be effectively controlled by a low-frequency THz field with amplitudes below 50 kV/cm. The THz field controls the electron–hole separation modifying decoherence and the irreversibility of carrier generation.enghttps://creativecommons.org/licenses/by/4.0/540530Charge carriersGallium arsenideIII-V semiconductorsInfrared devicesNonlinear opticsUltrafast lasersCarrier generationCondensed matterDriving frequenciesElectron-hole separationInterband tunnelingMid-infrared pulseNear infrared pulseTransverse optical phononsTerahertz spectroscopyarticleelectronexcitationinfrared radiationnonlinear systemphononterahertz spectroscopyArticle