arXiv subjects

Stephan Jauernik

Publications and source records attributed to Stephan Jauernik.

4 recordsLinked to original sources

arXiv2026

Coherent Phonon-Driven Band Renormalizations in 1T$'$-MoTe$_2$

Here, we investigate phonon mode- and electron band-selective electron-phonon couplings in centrosymmetric 1T$'$-MoTe$_2$ using time- and angle-resolved photoemission spectroscopy combined with frequency-domain analysis. Femtosecond near-infrared pulses excite coherent $A_g$-symmetric phonon modes at 2.34 THz, 3.34 THz, and 3.86 THz, which manifest as oscillatory modulations in photoemission intensity and binding energy across the valence bands. Pixel-wise Fourier analysis using recently developed methodologies reveals pronounced band selectivity with distinct coupling strengths for different electronic states and phonon modes, enabling the evaluation of band-renormalization amplitudes in the range of few meV. Ab initio calculations qualitatively reproduce the experimentally observed coupling patterns and relative trends, demonstrating the capability of combined experimental and theoretical approaches to resolve ultrafast electron-phonon interactions in quantum materials.

cond-mat.mtrl-sci↗

arXiv2025

Origin of phonon decoherence

Phonon decoherence determines the characteristic timescales over which coherent lattice vibrations decay, making it a crucial process for understanding the non-equilibrium dynamics of crystal lattices after excitation by a pump pulse. Here, we report a theoretical and computational investigation of the origin of phonon decoherence within a first-principles many-body framework. We derive quantum kinetic equations for the dynamics of coherent phonons by explicitly accounting for dissipation processes induced by electron-phonon and phonon-phonon interactions. The decoherence rate and frequency renormalization are formulated in terms of the non-equilibrium phonon self energy, providing a framework amenable for ab initio calculations. To validate this approach, we conduct a first-principles study of phonon decoherence for the elemental semimetals antimony and bismuth. The robust agreement with available temperature- and fluence-dependent experimental data confirms the accuracy of our theoretical and computational framework. More generally, our findings reveal that either electron-phonon and phonon-phonon coupling can prevail in determining the decoherence time, depending on the temperature and driving conditions. Overall, this work fills a critical gap in the theoretical understanding of phonon decoherence, providing a predictive framework for determining the timescales of light-induced structural dynamics in driven solids.

cond-mat.str-el↗

arXiv2024

Ultrafast low-energy photoelectron diffraction for the study of surface-adsorbate interactions with 100 femtosecond temporal resolution

An ultrafast photoemission-based low-energy electron diffraction experiment with monolayer surface sensitivity is presented. In a first experiment on tin-phthalocyanine adsorbed on graphite, we demonstrate a time resolution of approx. 100 fs. Analysis of the transient photoelectron diffraction signal indicates a heating of the adsorbate layer on a time scale of a few ps, suggesting coupling to phononic degrees of freedom of the substrate as the primary energy transfer channel for the vibrational excitation of the adsorbate layer. Remarkably, the transient photoelectron diffraction signal not only provides direct information about the structural dynamics of the adsorbate, but also about the charge carrier dynamics of the substrate. The presented concept combined with momentum microscopy could become a versatile tool for the comprehensive investigation of the coupled charge and vibrational dynamics of relevance for ultrafast surface processes.

cond-mat.mes-hall↗

arXiv2020

A combined laser-based ARPES and 2PPES study of Td-WTe$_2$

Laser-based angle-resolved photoemission spectroscopy (ARPES) and two-photon photoemission spectroscopy (2PPES) are employed to study the valence electronic structure of the Weyl semimetal candidate Td-WTe$_2$ along two high symmetry directions and for binding energies between $\approx$ -1 eV and 5 eV. The experimental data show a good agreement with band structure calculations. Polarization dependent measurements provide furthermore information on initial and intermediate state symmetry properties with respect to the mirror plane of the Td structure of WTe$_2$.

cond-mat.mtrl-sci↗