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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

The magic of non-equilibria

We identified two intrinsic timescales of the laser-induced phase transition in FeRh: Ferromagnetic domains form significantly faster after direct laser excitation compared to slow near-eq. heating.

Size does matter!

We demonstrate the acceleration of the laser-induced first-order antiferromagnetic-to-ferromagnetic phase transition by plasmonic absorption in FeRh nanoislands compared to continous thin films.

Resonant phase-matched strain pulses are the best

We identify the driving mechanisms of laser-induced magnetic precession in nickel films using tailored nanoscale metal heterostructures that help to shape the strain pulses and control the heat flow.

A magnetic multilayer sample hit by two consequtive laser pulses and probed by MOKE.

Hit me baby one more time!

Hitting a ferromagnet once can induce magnetic precession, hitting it twice cannot only undo or enhance the first hit, but it also sheds light onto the governing microscopic mechanisms.

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.