2023-04-12
How electrons dress up in light
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In close collaboration with the group of Ulrich Höfer (University of Marburg), we observed the ultrafast birth, rise, and collapse of a Floquet-Bloch band structure, for the first time. Angle-resolved photoemission spectroscopy combined with atomically strong light fields revealed that Floquet-Bloch bands form already after a single optical cycle and play an intriguing role in high-harmonic generation. These surprising findings pave the way to tailored quantum functionalities and ultrafast electronics. Theoretical modeling by Michael Schüler (Paul Scherrer Institute, Villigen) and Michael Sentef (MPI Hamburg) convincingly supported the conclusions.
The results have been published in Nature. |
Image (from left to right, top): Manuel Meierhofer, Lukas Kastner, Rupert Huber (professor), Markus Huber, Martin Zizlsperger, Simon Maier, (bottom:) Johannes Hayes, Marlene Liebich...
Directly watching in slow-motion videos how electrons move in quantum mechanical orbitals and how this motion shapes the functionalities of condensed matter has been a dream shared by all natural and life sciences. Yet, this vision comes with the daunting challenge of mapping the microscopic structure of electronic orbitals with simultaneous ultrafast time resolution. 
Im Rahmen des regensburgweiten Events "Nacht schafft Wissen!" wurde Interessierten und Physikbegeisterten in Führungen durch unsere Kellerlabore Ultrakurzzeit- und Laserphysik an spannenden Vorführexperimenten nähergebracht.
Together with our partners, 
Together with the group of Mackillo Kira (Michigan), we use multi-terahertz light fields to force electron-hole pairs in semiconductors onto closed recollision paths. Attosecond clocking of these trajectories reveals how many-body correlations like strong Coulomb interactions modify the charge carrier dynamics. This novel concept offers a completely new access to exotic phase transitions and quantum dynamics important for future electronic and quantum-information technologies.
We congratulate Joshua Mornhinweg on winning the first prize of the best student paper award of the 2022 International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) in Delft with his talk titled nonlinear subcycle dynamics of ultrastrong light-matter interaction. The prize honours original contributions to the conference from outstanding student attendees....
Image (from left to right): Manuel Meierhofer, Martin Zizlsperger, Felix Schiegl, Rupert Huber (professor), Christian Meineke, Johannes Hayes, Marlene Liebich
We studied the ultrafast dynamics of intersubband polaritons in the mid-infrared together with the groups of Raffaele Colombelli (Paris), Christoph Lange (Dortmund) and Iacopo Carusotto (Trento). Stimulated scattering occurs between these polaritons for resonant excitation, which we observe directly within the polaritonic bandstructure. This scattering mechanism could enable Bose-Einstein-condensates of intersubband polaritons for novel quantum computers and on-chip mid-infrared light sources.
In collaboration with the group of Heiko Weber (Friedrich-Alexander-Universität Erlangen-Nürnberg) we investigated mid-infrared light-field-driven tunneling currents in a Schottky diode, consisting of epitaxial graphene on silicon carbide. Our study gives insights into the intrinsic speed limits of rectification currents in these devices and paves the way towards light-field-driven electronics with increased functionality, such as transistors and logic circuits.
We developed a novel, flexible and scalable emitter of extremely asymmetric and intense terahertz field transients together with the groups of Dominique Bougeard (UR) and Mackillo Kira (University of Michigan) as well as collaborators from the Helmut Schmidt University and the Justus Liebig University Gießen. Making use of shift currents and local charging dynamics in asymmetrically coupled epitaxial semiconductor heterostructures, we generated waveforms exhibiting less than an oscillation half-cycle, peak fields above 1.1 kV cm-1 and spectra spanning into the mid-infrared, marking a milestone for next-generation high-repetition-rate (multi-)terahertz sources.
In collaboration with the group of Ermin Malic (University of Marburg), we used ultrafast near-field microscopy to study the Mott transition of strongly-bound excitons in an atomically thin heterostructure of WSe2, unveiling pronounced nanoscale modulation in the dynamics of the transition. These findings underscore how nanoscale disorder plays a pivotal role in the dynamics of many-body phase transitions within a broad range of van der Waals materials.
