Bernd Beschoten gave a talk on the magnetic phases in bilayer graphene at the 2nd PASSQAL Workshop in Sendai. The workshop on "physics and application of spatial structures on spin, quantum state and light" was hosted by Prof. Makoto Kohda from Tohoku University.

Two of our group members, Hubert Dulisch and Christoph Stampfer, presented the recent results on bilayer graphene quantum dots in the SpinQubits workshop at the QTech-Bp meeting in Budapest. The conference was hosted at the Hungarian Academy of Sciences (an impressive building), celebrating its 200th anniversary alongside 100 years of quantum mechanics. Besides the stimulating scientific program, we had great fun reconnecting with former group members.

As part of this year’s RWTH anniversary celebration of the 1999 graduating class, it was a great pleasure for us to welcome some of the former graduates back to the research facility of the 2nd Institute of Physics. (The jubilarians from left to right: Dr. Michael Fischer, Dr. Frank Dillmann, Dr. Jochen Dreßen, Dr. Andreas Rosenberger. Hosts at the institute: Dr. Bernd Beschoten and Prof. Dr. emer. Gernot Güntherodt)."

Phys. Rev. Research 7, L032037 (2025)
We perform photoluminescence measurements on vacancy-related emitters in hexagonal boron nitride (hBN) that are notorious for their low quantum yields. The gating of these emitters via few-layer graphene electrodes reveals a reproducible, gate-dependent brightening of the emitter, which coincides with a change in the direction of the simultaneously measured leakage current across the hBN layers. At the same time, we observe that the relative increase of the brightening effect scales linearly with the intensity of the excitation laser. Both observations can be explained in terms of a photo-assisted electroluminescence effect. Interestingly, emitters can also show the opposite behavior, i.e., a decrease in emitter intensity that depends on the gate leakage current. We explain these two opposing behaviors by different concentrations of donor and acceptor states in the hBN and show that precise control of the doping of hBN is necessary to gain control over the brightness of vacancy-related emitters by electrical means. Our findings contribute to a deeper understanding of vacancy-related defect emitters in hBN that is necessary to make use of their potential in quantum information processing.

Phys. Rev. Phys. Educ. Res. 21 020110 (2025)
This exploratory field study investigates the integration of innovative forms of recitation tasks in a first-year introductory mechanics course, focusing on smartphone-based experimental tasks alongside programming and standard recitation tasks. Smartphones, combined with external sensor modules, serve as a gateway enabling students to conduct various low-cost and authentic physics experiments with first-hand data collection outside traditional lab settings. These tasks aim to enhance students’ agency in independent physics experimentation and enrich homework assignments by dissolving boundaries between lectures, recitation sessions, and traditional labs, and thereby linking theoretical and experimental aspects of undergraduate physics education. To explore this potential, we implemented and evaluated a sample set of nine smartphone-based experimental tasks and, for comparison, three programming tasks as weekly exercises in a first-year physics course at RWTH Aachen University. We investigated students’ perceptions of learning with these new tasks through twelve short surveys involving up to 188 participants, focusing on factors such as goal clarity, difficulty, or feasibility at home. In two additional surveys with 108 and 78 participants, students assessed affective responses to the smartphone-based experimental tasks relative to the programming and standard recitation tasks. Our findings indicate that the smartphone-based experimental tasks were generally well-suited to the students and tended to outperform the programming tasks in terms of perceptions of learning with the tasks and affective responses. Overall, students responded positively to the new experimental tasks, with perceptions comparable to, or only partly below, those of long-established standard recitation tasks. These results suggest that smartphone-based experimental tasks can be successfully integrated into teaching and contribute to refining traditional recitation tasks. Students’ differentiated perceptions of the three task types investigated offer valuable insights into how students perceived technology-enhanced recitation tasks in terms of feasibility, engagement, and instructional value. This provides a meaningful basis for instructors and researchers aiming to design more effective and student-centered learning environments in undergraduate physics education.

Phys. Rev. B 112, 035409 (2025)
The valley degree of freedom in 2D semiconductors, such as gapped bilayer graphene (BLG) and transition metal dichalcogenides, is a promising carrier of quantum information in the emerging field of valleytronics. While valley dynamics have been extensively studied for moderate band gap 2D semiconductors using optical spectroscopy techniques, very little is known about valley lifetimes in narrow band gap BLG, which is difficult to study using optical techniques. Here, we report single-particle valley relaxation times (T₁) exceeding several microseconds in electrostatically defined BLG quantum dots using a pulse-gating technique. The observed dependence of T₁ on perpendicular magnetic field can be understood qualitatively and quantitatively by a model in which T₁ is limited by electron-phonon coupling. We identify the coupling to acoustic phonons via the bond length change and via the deformation potential as the limiting mechanisms.

This week we had the pleasure of welcoming Rahimkulov Margarita and Bálint Szentpéteri from the Quantum Transport Laboratory of Szabolcs Csonka at Budapest University of Technology and Economics (BME). During their stay, they visited our labs and exchanged ideas with the bilayer graphene quantum dot team and others.