Regensburg 2025 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 23: Poster Ultrafast Electron Dynamics
O 23.8: Poster
Montag, 17. März 2025, 18:00–20:00, P2
Ultrafast current response of solids - limits of quasi-classic current formula — •Jelena Schmitz, Adrian Seith, Jan Wilhelm, and Ferdinand Evers — Institute of Theoretical Physics and Regensburg Center for Ultrafast Nanoscopy (RUN), University of Regensburg, D-93053 Regensburg, Germany
In a quasi-classical picture, the velocity of an electron with crystal momentum k is given by [1] vn(k) = ∂ єn(k) / ∂ k+ q E(t) × Ωn(k) (1), where єn(k) denotes the band structure and Ωn(k) the Berry-curvature associated with the n-th band. Expression (1) is expected to describe the material’s current response to a time-dependent external field, E(t), in the limit of slow and weak driving. Motivated by recent progress in generating ultrashort laser pulses, we study the limits of applicability of Eq.(1) in the limit of fast and strong driving. To this end, we adopt the framework of the Semiconductor-Bloch Equations (SBE) [2,3]; we derive Eq.(1) using a perturbative expansion of the SBE leading to analytical expressions for the limits of applicability and compare Eq.(1) with numerical solutions of the full SBE [4].
For massive Dirac Fermions, we find the bandgap energy and the Fermi level as the parameters determining the frequency domain as well as the maximum E-field strength for which the SBEs lead to matching results with Eq.(1).We also calculate corrections to Eq.(1) that enable us to identify Berry-curvature terms at higher frequencies.[1] Xiao, Di et. al., Rev. Mod. Phys. 82, 1959 (2010) [2] Schmitt-Rink, Stefan et. al., Phys. Rev. B 37, 941 (1988) [3] Wilhelm, Jan et. al., Phys. Rev. B 103, 125419 (2021) [4] https://github.com/ccmt-regensburg/CUED/
Keywords: quasi-classic; Berry-curvature; Semiconductor-Bloch Equations; Ultrafast dynamics; photocurrent