arXiv subjects

Markus Uehlein

Publications and source records attributed to Markus Uehlein.

6 recordsLinked to original sources

arXiv2026

Interplay of non-local transport and local scattering during electron thermalization and spatial equilibration in laser-excited metals

Ultrafast laser excitation of metals induces electronic nonequilibrium both in space and locally in the energy distribution. The subsequent dynamics are governed by the interplay between non-local transport and local scattering of hot electrons, yet combined microscopic descriptions of these processes remain sparse. Here, we disentangle the influence of these processes on thermalization using a reformulation of the Boltzmann transport equation in energy space that consistently describes both spatial equilibration and scattering through full collision integrals. Our results reveal that transport accelerates the apparent thermalization observed at the irradiated surface by removing athermal carriers, while the same spatial redistribution delays complete equilibration of the full electron system. We analyze the experimentally accessible energy-dependent dynamics at the front and back surface and find that the dominant process varies, depending on both position and on the energetic window. Overall, our work improves the understanding of the interplay of electronic nonequilibrium processes occurring in optically thick laser-driven systems with relevant implications for future electronic applications.

cond-mat.mtrl-sci↗

arXiv2026

From Code to Figure: A FAIR-Aligned Data Provenance Chain for Reproducible Simulation Research in Numerical Physics

Computational physics increasingly depends on large simulation datasets generated by software that remains under active development for many years. In such settings, reproducibility requires not only well documented data but also explicit links between code versions, simulation inputs, generated outputs, analysis steps, and published figures. Here, we present an integrated workflow for reproducible and FAIR-aligned simulation research in numerical physics. We describe how version control, code review, automated testing, structured logging, metadata-rich output, and standardized post-processing can be combined to support traceability from software development to publication. The presented concepts demonstrated for one particular simulation framework are broadly applicable to computational physics and other data-intensive areas of scientific computing.

physics.comp-ph↗

arXiv2026

Competing thermalization pathways of photoexcited hot electrons

Photoexcited hot carriers in solids can drive processes, such as photocatalytic reactions on the surface, beyond those available in thermal equilibrium. Hot-electron-mediated reaction pathways are limited by the thermalization of the nonequilibrium electron distribution through microscopic scattering events. Commonly, thermalization is exclusively attributed to electron-electron scattering, whereas electron-phonon scattering is considered relevant mainly for the energy equilibration with the lattice. With a kinetic model based on full Boltzmann collision integrals, we demonstrate that each scattering mechanism alone can thermalize the electron distribution, albeit along different trajectories in phase space. We find an opposite dependence on the excitation strength of the respective thermalization times and show that both processes can become comparable for weak excitations, corresponding to a sample temperature increase of a few Kelvin. Our results unravel the contributions of electron-electron and electron-phonon scattering to the thermalization across the full range of experimental excitation strengths up to the melting regime, thus facilitating the prediction of thermalization times for hot-carrier-based applications.

cond-mat.mtrl-sci↗

arXiv2026

Thermalization of Optically Excited Fermi Systems: Electron-Electron Collisions in Solid Metals

Ultrafast optical excitation of metals induces a non-equilibrium energy distribution in the electronic system, with a characteristic step-structure determined by Pauli blocking. On a femtosecond timescale, electron-electron scattering drives the electrons towards a hot Fermi distribution. In this work, we present a derivation of the full electron-electron Boltzmann collision integral within the random-k approximation. Building on this approach, we trace the temporal evolution of the electron energy distribution towards equilibrium, for an excited but strongly degenerate Fermi system. Furthermore, we examine to which extent the resulting dynamics can be captured by the numerically simpler relaxation time approach, applying a constant and an energy-dependent relaxation time derived from Fermi-liquid theory. We find a better agreement with the latter, while specific features caused by the balance of scattering and reoccupation can only be captured with a full collision integral.

cond-mat.mtrl-sci↗

arXiv2023

Time-resolved spectral densities of non-thermal electrons in gold

Noble-metal nanoparticles for photocatalysis have become a major research object in recent years due to their plasmon-enhanced strong light-matter interaction. The dynamics of the hot electrons in the noble metal are crucial for the efficiency of the photocatalysis and for the selective control of reactions. In this work, we present a kinetic description of the non-equilibrium electron distribution created by photoexcitation, based on full energy-resolved Boltzmann collision integrals for the laser excitation as well as for the electron-electron thermalization. The laser-induced electronic non-equilibrium and the inherently included secondary electron generation govern the dynamics of non-thermal electrons. Applying our method to gold, we show a significant dependence of hot electron dynamics on kinetic energy. Specifically, the timescales of the relaxation as well as the qualitative behavior are depending on the evaluated energy window. During the thermalization processes there are cases of increasing electron density as well as of decreasing electron density. Studying the influence of excitation parameters, we find that the photon energy and the fluence of the exciting laser can be tuned to influence not only the initial excitation but also the subsequent characteristics of the time-resolved electronic spectral density dynamics. The electronic thermalization including secondary electron generation leads to time-dependent spectral densities which differ from their specific final equilibrium values for picoseconds after irradiation ended.

physics.app-ph↗

arXiv2021

Implementation of the electronic non-equilibrium in the two-temperature model

We investigate a temperature-based model, called extended two-temperature model (eTTM), that describes the electronic non-equilibrium and its effect on energy dissipation in metals after ultrashort laser excitation. We derive and discuss improvements in comparison to published versions of this model [E. Carpene, Phys. Rev. B 2006, 74, 024301; G. Tsibidis, Appl. Phys. A 2018, 124, 311]. The comparison of the results of the eTTM with results of the well-known two-temperature model (TTM) shows a delayed increase of the electronic temperature when being calculated with the eTTM. We find a good agreement in the non-equilibrium energy distribution after absorption of photons with results from a kinetic description using a Boltzmann collision term. The model provides a convenient tool for fast calculation of features of the non-equilibrium electrons. As an example we inspect the dynamics of high-energy electrons observable in photo-electron spectroscopy and demonstrate the advantage of the eTTM over the conventional two-temperature model.

cond-mat.mtrl-sci↗