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In semiconductors and semimetals, strong THz electric fields can induce a controlled coherent motion of the electrons in the conduction band, via ballistic excitation. In the first picoseconds after THz excitation, the nonlinearities induced by this coherent excitation prevail before more incoherent high field effects start dominating the nonlinear response. Disentangling these different nonlinear contributions with 2D THz spectroscopy, we follow the trajectory of the out-of-equilibrium electron population in low-bandgap semiconductor InSb and. We then extract information on the conduction band curvature and evaluate its anharmonicity and its anisotropy, close to the Gamma-point. |
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