Current events
Next talk on Tuesday in 2 days by Ananya Singh.
News 28.06.2024
Professor Slava Rotkin from Penn State University completes sabbatical with our research group
Site Content:
30.01.2023
Workshop of the Aachen Graphene & 2D Materials Center
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!
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27.01.2023
Special Recognition for Luca Banszerus from the German Academic Scholarship Foundation
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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.
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25.01.2023
New publication: Putting High-Index Cu on the Map for High-Yield, Dry-Transferred CVD Graphene
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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.
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19.01.2023
New publication: Phonon-mediated room-temperature quantum Hall transport in graphene
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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.
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02.12.2022
Christoph Stampfer has been appointed Program Chair of 6th Graphene Flagship Japan-EU Workshop
Christoph Stampfer has been appointed as one of the four program chairs for the 6th Graphene Flagship Japan-EU Workshop on graphene and related 2D materials, which will be held 25-26 May 2023 at Tokyo (Japan). The workshop will provide a forum to discuss the latest developments in graphene and 2D materials research. For more details see here.
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25.10.2022
New publication: Experimental Observation of ABCB Stacked Tetralayer Graphene
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ACS Nano 10, 16617 (2022) In tetralayer graphene, three inequivalent layer stackings should exist; however, only rhombohedral (ABCA) and Bernal (ABAB) stacking have so far been observed. The three stacking sequences differ in their electronic structure, with the elusive third stacking (ABCB) being unique as it is predicted to exhibit an intrinsic bandgap as well as locally flat bands around the K points. Here, we use scattering-type scanning near-field optical microscopy and confocal Raman microscopy to identify and characterize domains of ABCB stacked tetralayer graphene. We differentiate between the three stacking sequences by addressing characteristic interband contributions in the optical conductivity between 0.28 and 0.56 eV with amplitude and phase-resolved near-field nanospectroscopy. By normalizing adjacent flakes to each other, we achieve good agreement between theory and experiment, allowing for the unambiguous assignment of ABCB domains in tetralayer graphene. These results establish near-field spectroscopy at the interband transitions as a semiquantitative tool, enabling the recognition of ABCB domains in tetralayer graphene flakes and, therefore, providing a basis to study correlation physics of this exciting phase.
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24.10.2022
New publication: The Reststrahlen Effect in the Optically Thin Limit: A Framework for Resonant Response in Thin Media
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Nano Letters 22, 8389 (2022) Sharp resonances can strongly modify the electromagnetic response of matter. A classic example is the Reststrahlen effect – high reflectivity in the mid-infrared in many polar crystals near their optical phonon resonances. Although this effect in bulk materials has been studied extensively, a systematic treatment for finite thickness remains challenging. Here we describe, experimentally and theoretically, the Reststrahlen response in hexagonal boron nitride across more than 5 orders of magnitude in thickness, down to a monolayer. We find that the high reflectivity plateau of the Reststrahlen band evolves into a single peak as the material enters the optically thin limit, within which two distinct regimes emerge: a strong-response regime dominated by coherent radiative decay and a weak-response regime dominated by damping. We show that this evolution can be explained by a simple two-dimensional sheet model that can be applied to a wide range of thin media.
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14.09.2022
Welcome to Mr. Saketh Ravuri and Ms. Priyanka Mondal
Mr. Saketh Ravuri and Ms. Priyanka Mondal have joined the 2D Materials and Quantum Devices Group at the 2nd Institute of Physics A for a seven-month research staying supported by a DAAD KOSPIE scholarship. Mr. Ravuri and Ms. Mondal are currently pursuing a Master in Physics at the Indian Institute of Technology in Madras and Kharagpur, India, respectively. In Aachen, they will work on their Master Thesis project, focusing on bilayer graphene quantum devices and on MoSe2-WSe2 in-plane heterostructures.
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