Forschung

Der von der DFG geförderte Exzellenzcluster „Center for Chiral Electronics (externer Link, öffnet neues Fenster)“ (CCE) bringt führende Forschende aus Physik und Chemie in Halle (Saale), Berlin und Regensburg zusammen.

CCE wird das einzigartige Potenzial der Chiralität in Festkörper- und molekularen Systemen erforschen, um elektronische Technologien der nächsten Generation zu entwickeln – leistungsstark und energieeffizient – und damit der wachsenden Nachfrage nach einer nachhaltigeren digitalen Infrastruktur gerecht zu werden.

Zusammen mit Leo Gross (externer Link, öffnet neues Fenster) (IBM Zurich) und Diego Peña (externer Link, öffnet neues Fenster) (University Santiago de Compostela) erhielten wir einen ERC Synergy Grant für unser Projekt“Molecular Devices by Atom Manipulation” (MolDAM).

Mehr Informationen über ERC Synergy Grants. (externer Link, öffnet neues Fenster)

Wir danken der Deutschen Forschungsgemeinschaft herzlich für die Förderung im Rahmen des SFB 1277 (externer Link, öffnet neues Fenster): „Emergente relativistische Effekte in kondensierter Materie“ sowie der Forschungsprojekte.
 

RTG 2905 “Ultrafast Nanoscopy” (externer Link, öffnet neues Fenster)

Die folgenden Inhalte sind nur auf Englisch verfügbar, da Englisch die internationale Standardsprache der Wissenschaft ist.

Alternate-Charging STM (AC-STM): (externer Link, öffnet neues Fenster)

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): (externer Link, öffnet neues Fenster)

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): (externer Link, öffnet neues Fenster)

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 (externer Link, öffnet neues Fenster)

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.

Unsere Mikroskope werden unter Ultrahochvakuum- (UHV) und kryogenen Temperaturen (10° K und darunter) betrieben. Dies ermöglicht die Untersuchung einzelner Moleküle unter sauberen und stabilen Bedingungen.