# Ultrafast electron-electron scattering in metallic phase of 2H-NbSe$\_2$ probed by high harmonic generation Source: [Ultrafast electron-electron scattering in metallic phase of 2H-NbSe$\_2$ probed by high harmonic generation]() Collection index: [llms.txt]() Data updated: 2025-10-25T04:22:23.883Z Authors: K. S. Takeda, K. Uchida, K. Nagai, S. Kusaba, K. Tanaka Published: 2023-02-10T00:08:00.000Z ## Abstract Electron-electron scattering on the order of a few to tens of femtoseconds plays a crucial role in the ultrafast electron dynamics of conventional metals. When mid-infrared light is used for driving and the period of light field is comparable to the scattering time in metals, unique light-driven states and nonlinear optical responses associated with the scattering process are expected to occur. Here, we use high-harmonics spectroscopy to investigate the effect of electron-electron scattering on the electron dynamics in thin film 2H-NbSe$\_2$ driven by a mid-infrared field. We observed odd-order high harmonics up to 9th order as well as a broadband emission from hot electrons in the energy range from 1.5 to 4.0 eV. The electron-electron scattering time in NbSe$\_2$ was estimated from the broadband emission to be almost the same as the period of the mid-infrared light field. A comparison between experimental results and a numerical calculation reveals that a kind of resonance between scattering and driving enhances the non-perturbative behavior of high harmonics in metals, causing a highly non-equilibrium electronic state corresponding to several thousand Kelvin. ## Recorded benchmark results A research result applies to its stated dataset, split, metric and evaluation configuration. Compare like-for-like settings, preserve the metric's unit and direction, and distinguish paper-reported results from independent reproduction. The best result recorded here is not a claim of exhaustive, current global coverage. ## Original sources and implementation [Original paper]() [PDF]()