Publications

The propagation of magnons in temperature gradients is investigated within the framework of an atomistic spin model with the stochastic Landau-Lifshitz-Gilbert equation as underlying equation of motion. We analyze the magnon accumulation, the magnon temperature profile, as well as the propagation length of the excited magnons. The frequency distribution of the generated magnons is investigated in order to derive an expression for the influence of the anisotropy and the damping parameter on the…

Acoustic frequency combs are optically excited and detected in silicon membranes covered with thin aluminum layers by femtosecond pump-probe spectroscopy. The various frequency combs consist of 11 up to 45 modes ranging in frequency from 10 up to 500 GHz. Evaluating the different modes of the combs allows us to quantify the dynamic properties of this two-layer system with great precision.

Deviations of the frequencies of higher modes from a linear relation can be quantitatively understood. The…

We use ultrafast pump-probe pectroscopy to study the mechanical vibrations in the time domain of doubly clamped silicon nitride beams. Beams with two different clamping conditions are investigated. Finite element method calculations are performed to analyse the mode spectra of both structures.

By calculating the strain integral on the surface of the resonators, we are able to reproduce the effect of the detection mechanism and identify all the measured modes. We show that our spectroscopy…

The possibility of fabricating electronic devices with functional building blocks of atomic size is a major driving force of nanotechnology. The key elements in electronic circuits are switches, usually realized by transistors, which can be configured to perform memory operations. Electronic switches have been miniaturized all the way down to the atomic scale.

However, at such scales, three-terminal devices are technically challenging to implement. Here we show that a metallic atomic-scale…

Atomic and single-molecule junctions represent the ultimate limit to the miniaturization of electrical circuits. They are also ideal platforms for testing quantum transport theories that are required to describe charge and energy transfer in novel functional nanometer-scale devices. Recent work has successfully probed electric and thermoelectric phenomena in atomic-scale junctions. However, heat dissipation and transport in atomic-scale devices remain poorly characterized owing to experimental…

We study the relaxation of coherent acoustic phonon modes with frequencies up to 500 GHz in ultrathin free-standing silicon membranes. Using an ultrafast pump-probe technique of asynchronous optical sampling, we observe that the decay time of the first-order dilatational mode decreases significantly from ∼4.7  ns to 5 ps with decreasing membrane thickness from ∼194 to 8 nm.

The experimental results are compared with theories considering both intrinsic phonon-phonon interactions and extrinsic…

While many aspects in physics can be treated with single-particle models, many-body correlations are of great interest because only by taking them into account intriguing effects like superconductivity, heavy Fermion systems, and the Kondo effect can be explained. The Kondo effect arises due to the interaction between a localized spin and the electrons of a surrounding host and manifests itself as a characteristic zero bias anomaly in tunneling experiments. Studies of magnetic impurities by…

We study finite-time Landau-Zener transitions at a singlet-triplet level crossing in a GaAs double quantum dot, both experimentally and theoretically. Sweeps across the anticrossing in the high driving speed limit result in oscillations with a small visibility.

Here we demonstrate how to increase the oscillation visibility while keeping sweep times shorter than T₂^* using a tailored pulse with a detuning dependent level velocity. Our results show an improvement of a factor of ∼2.9 for the…

We study time-dependent electronic and spin transport through an electronic level connected to two leads and coupled with a single-molecule magnet via exchange interaction. The molecular spin is treated as a classical variable and precesses around an external magnetic field.

We derive expressions for charge and spin currents by means of the Keldysh nonequilibrium Green's functions technique in linear order with respect to the time-dependent magnetic field created by this precession. The…