On the 24th, Proceedings of the National Academy of Sciences of the U.S.A. published a paper on twisted bilayer graphene near the second magic angle, to which our group contributed. The manuscript is entitled, Multiple flat bands and topological Hofstadter butterfly in twisted bilayer graphene close to the second magic angle. The work discusses measurements of multiple flat bands in high-quality twisted bilayer graphene close to the theoretically predicted second magic angle. These well-isolated flat moiré bands host a nontrivial topology, which is evidenced by a connecting multiband Hofstadter butterfly spectrum. The manuscript provides a perspective for understanding the emergent quantum phases in twisted bilayer graphene and the fractal Hofstadter spectra of multiple topological bands.
Ph.D. student Giulio Romagnoli carried out transport measurements on twisted bilayer graphene here in Basel at 300 mK with first author Dr. Xiaobo Lu, who was affiliated with ICFO Barcelona at the time. The project was led by Prof. Dmitri Efetov of ICFO.
On the 3rd, group members met up for a farewell BBQ for Lorenzo Ceccarelli, who will soon start a job at Nanosurf in Liestal. The party also marked the 5th annual BBQ at the Birsköpfli park along the river. Although the weather and river did not fully cooperate, we had a relaxing time eating, drinking, and playing in the park. Thanks to all for a good time. Pictures are here. Lorenzo will have his last day in the group on the 9th. Thanks for everything, Lorenzo, and good luck in the new job!
This month, an interview of Prof. Poggio appeared in the newsletter of the the Condensed Matter Division (CMD) of the European Physical Society (EPS). See here.
Post-doctoral researcher and former Ph.D., Dr. Marcus Wyss, is taking a new job as an electron microscopy technician and researcher at the Nano Imaging Lab of the Swiss Nanoscience Institute. He will move just down the street to the Pharmazentrum and will be in charge of the SEM/FIB and TEMs. He will continue to collaborate with our group, especially on the FIBsuperProbes project. We wish you luck on the new position, Marcus, and look forward to continue working together!
On the 21st, Prof. Poggio gave a talk entitled, “Stability of Néel-type skyrmion lattice against oblique magnetic fields in GaV4S8 and GaV4Se8” at the 2021 Virtual MRS Spring Meeting. The talk was part of session NM04.01: Magnetic Skyrmions and Topological Effects in Materials and Nanostructures I. The talk focused on our recent measurements of the stability of the skyrmion lattice phase as a function of magnetic field angle and magnitude in Néel-type skyrmion hosts.
Ph.D student Mathias Claus started in our group in the middle of this month. Mathias did his Master thesis in our group on designing and fabricating nanometer-scale torsional resonators for torque magnetometry. He completed his Bachelor of Science in Nanoscience in 2020 and his and Masters of Science in Nanoscience in 2021, both here at the University of Basel. He will start in the group as a joint member of our group and the group of Prof. Ilaria Zardo.
On Wednesday the 24th, group members took advantage of the weather to walk up to the Hornfelsen overlook, just outside of Basel. There, we had a BBQ and enjoyed the sun. Afterwards, some group members kept walking up to St. Chrischona, and then back to the Department via Riehen and Lange Erlen. Thanks to all for a relaxing time. Pictures and movies are here.
Ph.D. student Nadine Leisgang of the Warburton Group appeared in a video put out by the NCCR QSIT on women in physics. Nadine has been working closely with our group, in particular with Ph.D. students Hinrich Mattiat and Lukas Schneider, on magnetic scanning probe experiments on 2D materials. See the video here.
Ph.D student Luca Forrer started in our group this month. Luca completed his Bachelor of Science in Nanoscience in 2019 and his and Masters of Science in Nanoscience in 2020, both here at the University of Basel. He will join our group as part of a joint project with the group of Prof. Dominik Zumbühl funded by the Swiss Nanoscience Institute.
On the 11th at 17:00 CET, Prof. Poggio gave a webinar on the Physics Today platform on the physics underlying magnetic imaging techniques, including MFM, scanning SQUID microscopy, and scanning NV-center microscopy. Dr. Jelena Trbovic of Zurich Instruments discussed how lock-in amplifiers can be used to enhance their sensitivity and contrast of such local measurements. See the webinar here.
On the 15th, Daniel Jetter officially joined our group as a Ph.D. student. Daniel has been working in our group since January 2020, when he started as a visiting Masters student, under the external supervision of Prof. Reinhold Kleiner at the University of Tübingen. He worked on the development of a nanometer-scale SQUID-on-cantilever probe for sensitive magnetic imaging. Daniel finished his Masters in earlier this month.
On February 11th at 17:00 CET, Prof. Poggio will give a webinar on the Physics Today platform on the physics underlying magnetic imaging techniques, including MFM, scanning SQUID microscopy, and scanning NV-center microscopy. He will discuss how to best apply these techniques to shed light on magnetization patterns, spin configurations, and current distributions in a number of exciting condensed matter systems. Dr. Jelena Trbovic of Zurich Instruments will also discuss how lock-in amplifiers can be used with such local probing techniques to enhance their sensitivity and contrast. Register here.
On the 4th, Physical Review B published our paper entitled, Magnetic anisotropy of individual maghemite mesocrystals. Maghemite mesocrystals are magnetic superstructures of maghemite nanoparticles, which are arranged in highly ordered lattices of up to a few micrometers in size. Although measurements on disordered ensembles have been carried out, determining the magnetic properties of individual mesoscopic crystals is challenging due to their small total magnetic moment. In our paper, we describe how to overcome these challenges by utilizing sensitive dynamic cantilever magnetometry to study individual mesocrystals.
Our measurements reveal an unambiguous cubic anisotropy, resulting from the crystalline anisotropy of the constituent maghemite nanoparticles and their alignment within the mesoscopic lattice. The signatures of anisotropy and its origins come to light because we combine the self-assembly of highly ordered mesocrystals with the ability to resolve their individual magnetism. This combination is promising for future studies of the magnetic anisotropy of other nanoparticles, which are too small to investigate individually.
Post-doc Dr. Boris Groß and Ph.D. student Simon Philipp carried out all of the DCM experiments, numerical simulations, and data analysis. External collaborators synthesized the mesocrystals.