arXiv subjects

Beatrice Andres

Publications and source records attributed to Beatrice Andres.

4 recordsLinked to original sources

arXiv2025

Magnon-mediated terahertz spin transport in metallic Gd|Pt stacks

We study femtosecond spin transport in a Gd|Pt stack induced by a laser pulse. Remarkably, the dynamics of the spin current from Gd to Pt suggests that its dominant driving force is the ultrafast spin Seebeck effect. As the contribution of a transient spin voltage in the metal Gd is minor, Gd acts akin a magnetic insulator here. This view is supported by time- and spin-resolved photoemission, which indicates that a buildup of spin voltage is suppressed by exchange scattering, leading to similar amplitudes and relaxation rates of hot majority- and minority-spin electron populations.

cond-mat.mes-hall↗

arXiv2024

Local work-function manipulation by external optical stimulation

Strongly differing static dipole moments of the trans and cis isomers of photochromic azobenzene allow for optical switching the work function of azobenzene-functionalized self-assembled monolayers (SAMs). We apply these properties in a fundamental experiment to manipulate the area size of the switched SAM. Azobenzene molecules were excited by ultraviolet laser illumination and the transient isomerization profile of the SAM was spatially resolved recording photoemission electron microscopy (PEEM) images. Thereby we demonstrate the spatial tuning of the SAM work-function and discuss the role of the laser spot-profile in generating sharp edges or gradual changes of the work function.

cond-mat.mes-hall↗

arXiv2021

The role of spin-lattice coupling for ultrafast magnetization changes in rare earth metals

By comparing femtosecond laser-pulse-induced spin dynamics in the surface state of the rare earth metals Gd and Tb we show that the spin polarization of the valence states in both materials decays with significantly different time constants of 15\,ps and 400\,fs, respectively. The distinct spin polarization dynamics in Gd and Tb are opposed by similar exchange splitting dynamics in the two materials. The different time scales observed in our experiment can be attributed to weak and strong $4f$ spin to lattice coupling in Gd and Tb suggesting an intimate coupling of spin polarization and 4f magnetic moment. While in Gd the lattice mainly acts as a heat sink, it contributes significantly to ultrafast demagnetization of Tb. This helps explain why all optical switching is observed in FeGd -- but rarely in FeTb-based compounds.

cond-mat.mes-hall↗

arXiv2021

Strong Momentum-Dependent Electron-Magnon Renormalization of a Surface Resonance on Iron

The coupling of fermionic quasiparticles to magnons is essential for a wide range of processes, from ultrafast magnetization dynamics in ferromagnets to Cooper pairing in superconductors. Although magnon energies are generally much larger than phonon energies, up to now their electronic band renormalization effect in ferromagnetic metals suggests a significantly weaker quasiparticle interaction. Here, using spin- and angle-resolved photoemission, we show an extraordinarily strong renormalization leading to replica-band formation of an iron surface resonance at ~200 meV. Its strong magnetic linear dichroism unveils the magnetic nature and momentum dependence of the energy renormalization. By determining the frequency- and momentum-dependent self-energy due to generic electron-boson interaction to compute the resultant electron spectral function, we show that the surface-state replica formation is consistent with strong coupling to an optical spin wave in a Fe thin film.

cond-mat.mes-hall↗