Charge and energy transfer processes at organic-metal interfaces are of key relevance in molecular electronics and functionalization of surfaces with molecular switches. Therefore the electronic structure and femtosecond electron dynamics of self-assembled monolayers (SAMs) of azobenzene-functionalized alkanethiols on gold have been investigated with time-resolved two-photon photoemission...
Controlling magnetic states of matter on ultrashort timescales is crucial to engineering the next-generation magnetic devices combining ultrafast data processing with ultrahigh-density data storage.
Here, we report on femtosecond laser-driven dynamics of multi-sublattice magnetic materials, with both ferromagnetic and antiferromagnetic coupling between sublattices, investigated using...
Using ultrashort X-ray pulses from the Linac Coherent Light Source we carried out a pump-probe resonant inelastic x-ray scattering (RIXS) experiment on Fe(CO)5 photodissociation in ethanol. This allowed us to follow the evolution of the valence electronic structure of the iron carbonyl species in an element- and chemical-selective way with a 300 fs (FWHM) time resolution. Supported by novel ab...
We investigate coherent phonon propagation in a thin film of ferroelectric Pb(Zr0.2Ti0.8)O3 (PZT) by ultrafast X-ray diffraction (UXRD) experiments, which are analyzed as time-resolved reciprocal space mapping (RSM) in order to observe the in- and out-of-plane structural dynamics simultaneously.[1] The mosaic structure of the PZT leads to a coupling of the excited out-of-plane expansion to...
In the last decade hard x-ray high kinetic energy photoelectron spectroscopy (HAXPES or HIKE) has led to a break-through in the field of photoemission due to its non destructive way of investigating the bulk electronic properties of materials and in particular buried interfaces in layered systems. Nanolayered systems are the keystones of current and future devices. The electronic, magnetic and...
Lattice vibrations after femtosecond laser excitation can be launched by different processes such as the relaxation of hot electrons or the coupling of the laser pulses to the lattice via nonlinear-optical mechanisms. The pathway and time scale of energy transfer form photonic excitation to the phononic subsystem is of fundamental interest to understand various physical phenomena like e.g....
Understanding ultrafast all-optical magnetization switching (AOS), i.e. the permanent reversal of the magnetization by the sole action of a femtosecond laser pulse in the absence of any applied magnetic field, is a challenging issue which could have tremendous impact for the magnetic recording industry. While a qualitative agreement between spin atomistic simulations and experiments exists[1],...
State-selected aligned and oriented molecular ensembles serve as ideal samples to study ultrafast molecular dynamics in the molecular frame. Possible probing mechanisms are the investigation of molecular-frame photoelectron angular distributions or the detection of structural changes via X-ray and electron diffraction.
We have developed techniques to manipulate the motion of molecules in...
The current status of project P2 “Ultrafast charge transfer and isomerization dynamics of molecules” will be presented. The goal is to resolve the early-stage dynamics of energy relaxation concomitant with structural rearrangements in Fe(CO)5 in the gas phase. Photoexcitation generates a metal-to-ligand charge transfer in Fe(CO)5 that launches a sequence of processes on time scales of 20-30 fs...
BiFeO3 had a deep impact in the field of multiferroics, since it is magnetic and ferroelectric at room temperature, opening a wide field of applications, e.g. for spintronics and memory devices which can be addressed both magnetically and electrically. Furthermore, it is highly desirable to photo-control the polarization and magnetization in BiFeO3 directly by ultrafast optical...
Experimentally determined adsorption geometries of molecular switches are essential both for understanding their functionalities and for benchmarking ab initio calculations. The prototypical molecular switch azobenzene is investigated on the Ag(111) surface by means of the normal incidence x-ray standing wave (NIXSW) technique and dispersion-corrected density functional theory (DFT)...
Motivated by the x-ray induced ultra-fast transient drop of optical reflectivity of semi-conductors, we performed time-resolved photoemission (trPES) experiments with x-ray pump x-ray probe in order to understand the x-ray induced changes in the electronic structure of GaAs(100). To accomplish our measurements we were using the split-and-delay unit at PG2 beamline at the free-electron laser...
Antiferromagnetic (AFM) materials have been predicted to show ultrafast magnetic dynamics since no macroscopic magnetization exists and dynamics might not be restricted by conservation of angular momentum. Out of recent studies investigating ferromagnetic materials like pure 4f elements (Gd,Tb,..) or a combination of 3d and 4f elements with (GdFeCo,..) it turned out that that the fast...
Liquid water is the single most important medium in which chemical and biological processes take place. Rather than acting as passive environment, the dynamics of water during chemical and biological processes play a fundamental role in the solvation and stabilization of reaction intermediate. The possibility to generate sub-ps and very intense THz pulses at free-electron lasers in full...
We designed and performed a time- and angle- resolved photoemission experiment to investigate the electronic structure of a ferromagnetic Gadolinium film during ultrafast laser-induced demagnetization and subsequent thermal recovery.
To get a complete picture of the magnetization dynamics we track the binding energy of the exchange-split valence band, which mediates the exchange interaction...
We present recent results from ultrafast laser-driven magnetization
dynamics experiments on the rare-earth local-moment ferromagnets
Gadolinium and Terbium. Our experiment combines angle-resolved photoemission
spectroscopy (ARPES) with the VUV photon energies and time resolution made possible by high-order harmonic generation to scrutinize the non-equilibrium band structure...
Over the past decade, femtosecond optical laser pulses have fueled the discovery of ultrafast spin dynamics in magnetic materials that go beyond our equilibrium understanding of magnetism. Many of these phenomena are potentially suitable for future technological applications. For example, fs optical laser pulses can act as a stimulus to reverse the magnetization direction in ferrimagnetic...
Time resolved photoemission from core levels (trPES) at FELs is a tool for studying surface dynamics in real-time. Basis for this is the sensitivity of core-levels to their chemical environment. By probing their spectral evolution after an ultra-short excitation one can get insight on both, electronically caused excitations (fs- up to several-ps time-scales) as well as responses of the crystal...
Magnetite (Fe3O4), is the first oxide where a relationship between electrical conductivity and fluctuating/localized charges was observed, with a drop in conductivity by two orders of magnitude at T=123K. The Verwey transition is accompanied by a structural change from monoclinic to cubic symmetry. Despite decades of research and indications that charge and orbital ordering play an important...
