January 2022: A new highly versatile laser system was installed in our lab. This femtosecond system, built by LIGHT CONVERSION, is part of the BMBF project TiNa II, a collaboration with the group of Prof. Lukas M. Eng at TU Dresden. It is destined for terahertz nanoscopy experiments using scanning near-field optical microscopy (THz-SNOM). With its repetition rate of 1 MHz and the ultra-wide wavelength range from 800 nm to 15 µm it will be the starting point for new, groundbreaking experiments at the TELBE facility.
November 2021: In our last beamtime of the year we attempted to use THz driving frequencies > 1.5 THz for the first time in a user beamtime. Thanks to improvements of the electron beam parameters, especially the bunch compression, by the ELBE team, we reached new record THz pulse energies: 6.1 µJ at 1.5 THz and 3.2 µJ at 2.4 THz.
October 2021: We published a new study on THz-driven charge carrier dynamics in topological insulators in NPJ Quantum Materials (DOI: 10.1038/s41535-021-00384-9). Disentangling bulk and surface dynamics in these complex materials is a highly relevant topic and the exact scattering mechanisms and timescales are still under debate. Using different complementary optical techniques, we demonstrate that after THz excitation carriers in the topological surface states relax much faster to their equilibrium state that those in the bulk (see also our press release).
- Our extensive study on THz-driven collective modes in various superconducting materials is available on the arXiv. In this long-term collaboration with Dr. Hao Chu, Prof. Stefan Kaiser et al. we employ the novel method of Higgs spectroscopy to disentangle the intricate interplay of collective modes in cuprate superconductors, identifying a Fano interference between the Higgs mode and charge density wave fluctuations.
- New article published on THz-driven dynamics in superconducting MgB2 in Physical Review B (DOI: 10.1103/PhysRevB.104.L140505) together with our colleagues from Cologne, Beijing and Dortmund.
- Our High power laser system (AMPHOS and White Dwarf from Class 5 Photonics) is installed in our main lab together with its HHG extreme UV source. For the first time, we are able to produce ultrashort XUV pulses for photoelectron emission spectroscopy in the TELBE lab.
April 2021: Our study on THz harmonics from electrically gated graphene layers is published in Science Advances (DOI: 10.1126/sciadv.abf9809). In this study, which is a collaboration with colleagues from Bielefeld, Barcelona and Berlin, we demonstrate how the efficiency of harmonics emission depends strongly on the carrier doping in the graphene layer. To show this we fabricated a device that enables direct tuning of the doping level by applying a small voltage to the graphene layer, as outlined in our press release.
- We welcome our new group member Dr. Thales de Oliveira. Thales has been a long-time colleague working with us on the THz-SNOM as a member of the TU Dresden. After the recent successful implementation of this technique at TELBE (manuscript in preparation) he joined our group full-time to implement and carry out challenging time-resolved THz nanoscopy experiments.
- Our new Coherent Astrella HE USP laser system (9 mJ pulse energy at 1 kHz, 800 nm wavelength) is installed in our new optical lab. We will use this system to generate high-field THz pulses that are complementary to our TELBE sources for various studies on THz-driven dynamics.
January 2021: Our new paper on THz harmonics generation in graphene-based metamaterials are published in ACS nano (DOI: 10.1021/acsnano.0c08106). By using thin metallic stripes as antennas, we show that harmonics emission is greatly enhanced for low driving fields. This approach may provide a viable path towards on-chip THz converters for high-speed optoelectronics, as outlined also in our press release.
September 2020: The results of our experiments demonstrating the inertial dynamics of electron spins driven by intense THz pulses are published in Nature Physics (DOI: 10.1038/s41567-020-01040-y). In a collaboration with Prof. Stefano Bonetti and other colleagues we were able to show that, by using the intense THz pulses from the TELBE source, the excited spins not only exhibit precessional motion, but also start to nutate. Why knowledge about these intricate spin dynamics may help in the development of new ultrafast and efficient data storage devices can be read in our press release.
- We have developed and implemented a novel method for measuring ultrafast laser-induced magnetization dynamics by transient THz emission spectroscopy. This technique for studying magnetic phase transitions is complementary to techniques based on the magneto-optic Kerr effect or X-ray magnetic circular dichroism. Our findings are published in Applied Physics Letters (DOI: 10.1063/5.0019663).
May 2020: Publication of new article on terahertz high harmonic generation in the Weyl semimetal Cd3As2 in Nature Communications (DOI: 10.1038/s41467-020-16133-8). For more details on how we use high-field THz pulses to drive carriers in this Dirac materials into the nonlinear regime, see our press release.
April 2020: New article on Higgs spectroscopy published together with our colleagues from Max Planck Institute for Solid State Research (MPI-FKF) and University of Tokyo in Nature Communications (DOI: 10.1038/s41467-020-15613-1). An overview of this newly developed technique that reveals the complex interactions of collective oscillations in superconductors can be found in our press release.