Once again, the Wissenschaftsnacht at RWTH Aachen proved to be a resounding success! This year, as in previous years, many members of our group contributed their time and expertise to make the evening a memorable experience for visitors.

Please find here a link to a youtube-video about it: "5 vor 12" - Die RWTH-Wissenschaftsnacht 2025

Nano Letters 25, 15809 (2025)
Polaritons in van-der-Waals materials (vdWMs) promise high confinement and multiple tailoring options by resonators and launching structures which conventionally require cumbersome lithography techniques. Optical programming of phase-change materials (PCMs) offers fast and reconfigurable fabrication of these structures. As the plasmonic PCM In₃SbTe₂ can be switched between a dielectric and metallic phase, In₃SbTe₂ is promising for optical programming of metallic launching structures to tailor and confine polaritons in vdWMs. Here, we combine the vdWM hexagonal boron nitride (hBN) with In₃SbTe₂ and optically program circular resonators for hBN’s phonon polaritons into In₃SbTe₂. We investigate the polariton resonators with near-field optical microscopy. Demonstrating the reconfigurability, we decrease the resonator diameter to increase the confinement up to λ/39 and achieve a quality factor of 72. Finally, we fabricate a focusing structure for hBN’s polaritons whose focal point we reconfigure. We promote In₃SbTe₂ as a versatile platform for rapid prototyping of polariton optics in vdWMs.

We are happy to share that Robin Dollemann, former postdoc in our group, has started his new position as Assistant Professor at HFML-FELIX in Nijmegen, Gelderland, Netherlands. His work will focus on developing fabrication methods for 2D materials and on low-temperature transport experiments in high magnetic fields.

Congratulations, Robin, on this exciting next step. We wish you a great start and all the best for this new chapter!

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.