Sebastian Staacks and Christoph Stampfer have been awarded the DPG Georg-Kerschensteiner Prize for the development of the free app phyphox. The award ceremony took place during the spring meeting of the Condensed Matter Division of the German Physical Society (DPG) in Dresden on the 28th of March.

The DPG's Georg-Kerschensteiner Prize honours outstanding achievements in physics didactics and/or physics teaching. More background and previous award winners can be found here (German only).

Alexander Rothstein just returned from a 3 weeks visit of the Quantum Nanoelectronics Group of Prof. Pablo Jarillo-Herrero at the Massachusetts Institute of Technology (MIT) in Boston (USA) for kicking-off a joined collaboration and for learning more about the fabrication of making large twisted bilayer graphene. Our 2D Materials and Quantum Devices Group at the RWTH thanks Dr. Aviram Uri (left) und Liqiao Xia (right) for sharing their knowledge.

Phys. Rev. B 107, 075420 (2023)
We present low-temperature Raman measurements on gate-tunable graphene encapsulated in hexagonal boron nitride, which allows us to study in detail the Raman G and 2D mode frequencies and linewidths as a function of the charge carrier density. We observe a clear softening of the Raman G mode (of up to 2.5 cm⁻¹) at low carrier density due to the phonon anomaly and a residual G mode linewidth of ≈3.5 cm⁻¹ at high doping. By analyzing the G mode dependence on doping and laser power we extract an electron-phonon-coupling constant of ≈4.4×10⁻³ (for the G mode phonon). The ultraflat nature of encapsulated graphene results in a minimum Raman 2D peak linewidth of 14.5 cm⁻¹ and allows us to observe intrinsic electron-electron scattering-induced broadening of the 2D peak of up to 18 cm⁻¹ for an electron density of 5×10¹²cm⁻² (laser excitation energy of 2.33 eV). Our findings not only provide insights into electron-phonon coupling and the role of electron-electron scattering in the broadening of the 2D peak but also crucially show the limitations when it comes to the use of Raman spectroscopy (i.e., the use of the frequencies and the linewidths of the G and 2D modes) to benchmark graphene in terms of charge carrier density, strain, and strain inhomogeneities. This is particularly relevant when utilizing spatially resolved 2D Raman linewidth maps to assess substrate-induced nanometer-scale strain variations.

We organized a 1-day Workshop of the Aachen Graphene & 2D Materials Center at RWTH SuperC. A full day to discuss open questions and emerging trends in the field. Thanks to all participants who contributed knowledge, ideas and complementary perspectives!

The Hirzebruch Doctoral Award jury from the German Academic Scholarship Foundation (German: Studienstiftung des deutschen Volkes, or Studienstiftung for short) gave special recognition ("besondere Anerkennung") to physicist Dr. Luca Felix Banszerus, whose dissertation "Gate-defined quantum dots in bilayer graphene" at RWTH Aachen University deals with quantum dots. With his research, he is a pioneer in the synthesis of quantum dots, which can potentially be used as building blocks in future quantum computers. Here some more information in German.

ACS Nano 17, 1229 (2023)
Reliable, clean transfer and interfacing of 2D material layers are technologically as important as their growth. Bringing both together remains a challenge due to the vast, interconnected parameter space. We introduce a fast-screening descriptor approach to demonstrate holistic data-driven optimization across the entirety of process steps for the graphene–Cu model system. We map the crystallographic dependences of graphene chemical vapor deposition, interfacial Cu oxidation to decouple graphene, and its dry delamination across inverse pole figures. Their overlay enables us to identify hitherto unexplored (168) higher index Cu orientations as overall optimal orientations. We show the effective preparation of such Cu orientations via epitaxial close-space sublimation and achieve mechanical transfer with a very high yield (>95%) and quality of graphene domains, with room-temperature electron mobilities in the range of 40000 cm²/(V s). Our approach is readily adaptable to other descriptors and 2D material systems, and we discuss the opportunities of such a holistic optimization.

Nat. Commun. 14, 318(2023)
The quantum Hall (QH) effect in two-dimensional electron systems (2DESs) is conventionally observed at liquid-helium temperatures, where lattice vibrations are strongly suppressed and bulk carrier scattering is dominated by disorder. However, due to large Landau level (LL) separation (~2000 K at B = 30 T), graphene can support the QH effect up to room temperature (RT), concomitant with a non-negligible population of acoustic phonons with a wave-vector commensurate to the inverse electronic magnetic length. Here, we demonstrate that graphene encapsulated in hexagonal boron nitride (hBN) realizes a novel transport regime, where dissipation in the QH phase is governed predominantly by electron-phonon scattering. Investigating thermally-activated transport at filling factor 2 up to RT in an ensemble of back-gated devices, we show that the high B-field behaviour correlates with their zero B-field transport mobility. By this means, we extend the well-accepted notion of phonon-limited resistivity in ultra-clean graphene to a hitherto unexplored high-field realm.