Research

The DFG-funded Cluster of Excellence “Center for Chiral Electronics (external link, opens in a new window)” (CCE) brings together leading researchers from physics and chemistry in Halle (Saale), Berlin, and Regensburg.  CCE will explore the unique potential of chirality in solid-state and molecular systems to develop next-generation electronic technologies – high-performance and energy-efficient – meeting  the growing demand for a more sustainable digital infrastructure.

Together with Leo Gross (external link, opens in a new window) (IBM Zurich) and Diego Peña (external link, opens in a new window) (University Santiago de Compostela) we receive an ERC Synergy Grant for our project “Molecular Devices by Atom Manipulation” (MolDAM).

More information on ERC Synergy Grants. (external link, opens in a new window)

We gratefully acknowledge funding from the Deutsche Forschungsgemeinschaft through SFB 1277 (external link, opens in a new window):
Emergent Relativistic Effects in Condensed Matter and the research projects

RTG 2905 “Ultrafast Nanoscopy” (external link, opens in a new window)

Alternate-Charging STM (AC-STM): (external link, opens in a new window)

AC-STM is a technique that enable orbital mapping on insulating substrates by synchronizing voltage pulses with an oscillating AFM tip. While traditional STM is restricted by conductive substrates, which lock molecule into fixed charge state. Synchronizing voltage pulses with the AFM enable alternate single electron charging on insulating surfaces – revealing previously inaccessible electronic redox transitions and molecular orbitals.

Excited State Spectroscopy (AC-STS): (external link, opens in a new window)

ESS is a single-molecule spectroscopy technique that employs controlled single-electron transfer to overcome the limitations of conventional methods, which typically capture only a subset of electronic transitions. By providing access to a broad array of quantum states, this method enables the precise determination of their energies and lifetimes.

Electron Spin Resonance - Atomic Force Microscopy (ESR-AFM): (external link, opens in a new window)

ESR-AFM combines the atomic precision of atomic force microscopy with electron spin resonance to detect spin transitions in individual molecules. A major challenge in current-based sensing, such as ESR-STM, is the inherent interaction between the tunneling current and the spin, which significantly limits coherence times. By utilizing a pump-probe AFM detection scheme, we enable coherent spin manipulation over tens of microseconds. This approach allows us to characterize quantum states with sub-nanoelectronvolt resolution, paving the way for investigating the atomistic origins of decoherence and conducting fundamental quantum-sensing experiments.

With state-of-the-art experimental setups combining low-temperature STM in an ultra-high vacuum environment with ultrashort laser pulses, we have developed techniques to resolve ultrafast dynamics of single-atom and single-molecule quantum systems on their intrinsic length, time and energy scales. In a collaboration with the group around Rupert Huber, we employ pulsed light sources of different frequencies to cover a range of time scales to observe dynamics ranging from attosecond charge transfer in atomic-resolution STM to motion of individual molecules on a surface or shifting electronic energy levels of atomic vacancies due to phononic motion. 

Terahertz STM (external link, opens in a new window)

Ultrashort terahertz pulses in the tunneling junction of an STM act as an ultrafast bias voltage. We have developed both lightwave-driven STM and lightwave-driven scanning tunneling spectroscopy to selectively address specific energy levels on timescales of the order of hundreds of femtoseconds. Thereby, we can take snapshots of molecular orbital densities in space allowing for molecular movies as well as snapshots of spatially confined states in energy to follow the temporal evolution of the local density of states. Investigated systems range from single molecules to atomic defects in transition metal dichalcogenides. 

In our lightwave-driven STM setup employing a magnetic field as an additional turning knob, we envision disentangling ultrafast dynamics on atomic scales with additional access to the spin degree of freedom.

Near- and mid-infrared STM

By utilizing near- and mid-infrared light pulses, we push the boundaries of the time resolution of lightwave-driven STM to the single-femtosecond and ultimately attosecond regime. This approach enables the observation of electron dynamics with combined sub-cycle temporal and atomic spatial resolution. We envision directly accessing dynamics such as electron propagation in nanostructures or chemical reactions on their intrinsic timescales.

Organic synthesis under UHV conditions confined to well-defined surfaces provides a powerful platform for the synthesis of by other means inaccessible compounds hosting fascinating properties like tailored edge states, exotic band structures, emergent π-magnetism and electron correlation. Our goal is the synthesis of novel compounds exhibiting such properties, which, among other challenges, requires the exploration of new reaction schemes. 

In addition, chemical reactions of organic molecules can be induced and controlled by applying voltage pulses with the STM tip. Well-known examples include the tautomerization of porphyrinoids or carbon-ring rearrangements. We aim to expand the range of tip-induced reactions while also deepening the understanding of the reaction mechanisms. Beyond STM and nc-AFM for structural characterization we employ Kelvin probe force spectroscopy (KPFS) to access charge states while light-wave driven STM may provide temporal resolution.

Our microscopes are operated under ultrahigh-vacuum (UHV) and cryogenic temperature (10K and below) conditions. This allows examining single molecules under clean and stable conditions.