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Welcome to the UDKM group website

We investigate coherent and incoherent non-equilibrium phenomena at the nanoscale initiated by various external stimuli, e.g. light and electromagnetic pulses. While incoherent processes transport heat and charges and may drive phase transitions and chemical reactions, coherent dynamics range from strain- and spin waves to strong coupling in exciton-plasmon systems.

Our focus is on a time-domain description of transporting and transforming energy among various excitations of matter. Transient strain and lattice dynamics in general are central observables in solids that are often connected and thus sensitive to other excitations such as hot electrons, lattice vibrations (phonons) and spin waves, electron-and phonon excitations, as well as  the latent heat of phase transitions. We aim at controlling strain waves in order to advance the field of nonlinear phononics and identify means of strain-assisted manipulation of magnetic and ferroelectric order. Polaritons, in particular plasmons, couple macroscopic light fields into the nanoworld, acting as an antenna for the chemical, electronic, magnetic or phononic excitations.

Typical research questions of the group involve ultrafast excitations, electron-phonon interaction, strain and heat as a driver of or sensor for ultrafast magnetism, ferroelectric switching and chemical reactions.

We attempt to create a special perspective on these phenomena by combining our experimental workhorses, which are ultrafast versions of x-ray diffraction, magneto-optics, transient absorption and reflection as well as time-resolved Raman scattering. We synthesize plasmonic nanostructures such as nanorods or nanostars embedded in soft condensed matter, e.g. nanolayered polyelectrolytes, whereas solid nanostructures are provided by our collaboration partners.

Recent publications

Photothermal reactors at the nanoscale

In this publication we present a nanoreactor based on catalytic metal particles embedded in a thermosensitive microgel, whose ability to catalyze reactions can be controlled by optically excitation.

Classical and quantum-mechanical treatment of absorption spectra of TDBC-coated gold nanoparticles.

The power (broadening) of the vacuum?

We present a new expression for the permittivity of an emitter shell around plasmonic nanoparticles. We thus reconcile Mie-Gans theory with experiments and show the influence of vacuum fluctuations.

X-ray signatures and layer-resolved laser-induced strain dynamics of a metallic multilayer stack.

This is how we roll ...

In our brandnew review we explain in detail how and why we use ultrashort x-ray pulses to infer the dynamical elastic behaviour of nanostructures excited by ultrashort laser pulses.

Laser-induced picosecond strain in the Pt-capped antiferromagnetic insulator NiO generates THz radiation.

ATTENTION: Trigger Warning!!

We demonstrate the generation of THz radiation triggered by laser excitation of a Pt-capped antiferromagnetic insulator NiO.

(Towards) shaping picosecond strain pulses

We exploit Dysprosium's giant magnetostriction to tune its laser-driven strain response by a magnetic field from expansion to contraction thus controlling the shape of emitted picosecond strain pulses

Sound vs Heat

In this joint publication Steffen clarifies whether elastic waves (sound) or heat generates the standing spin waves in a ferrimagnetic insulator.