Regensburg 2022 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 10: Focus Session: Superconductivity in 2d-Materials and their Heterostructures
TT 10.4: Hauptvortrag
Dienstag, 6. September 2022, 11:15–11:45, H3
Superconducting devices in magic-angle twisted bilayer graphene — •Elías Portolés1, Shuichi Iwakiri1, Giulia Zheng1, Kenji Watanabe2, Takashi Taniguchi2, Peter Rickhaus1, Thomas Ihn1, Klaus Ensslin1, and Folkert de Vries1 — 1Laboratory for Solid State Physics, ETH Zurich, Otto-Stern-Weg 1,Zurich, Switzerland — 2National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
Magic-Angle Twisted Bilayer Graphene (MATBG) hosts a range of physical phenomena that can be tuned by electrostatic doping [1]. Such in-situ tuning can be a crucial advantage of the material for hosting devices, which is the research direction we are currently exploring. We will first discuss the realization of a Josephson junction in this material. It is realized by combining gate-defined regions tuned to superconducting or insulating phases [2]. On top of the DC Josephson effect, we observe Shapiro steps and characterize the critical current hosted by the junction as a function of its length, exploiting the in-situ all-electrical tunability of the material. This confirms the potential of the material as a platform for versatile superconducting devices [2, 3]. In addition, we present a Superconducting Quantum Interference Device (SQUID) in MATBG [4], where the superconducting phase difference is controlled through the magnetic field. We observe magneto-oscillations of the critical current, demonstrating long-range coherence agreeing with an effective charge of 2e for the superconducting charge carriers. We tune to both asymmetric and symmetric SQUID configurations by electrostatically controlling the critical currents through the junctions. With this tunability, we study the inductances in the device, finding values of up to 2μH. Furthermore, we directly observe the current-phase relation of one of the Josephson junctions of the device.
[1] Cao, Y. et al. Unconventional superconductivity in magic-angle graphene superlattices. Nature 556, 43-50 (2018)
[2] de Vries, F.K. et al. Gate-defined Josephson junctions in magic-angle twisted bilayer graphene. Nature Nanotechnology 16, 760-763 (2021)
[3] Rodan-Legrain, D. et al. Highly tunable junctions and non-local Josephson effect in magic-angle graphene tunnelling devices. Nature Nanotechnology 16, 769-775 (2021)
[4] Portolés, E. et al. A Tunable Monolithic SQUID in Twisted Bilayer Graphene. arXiv:2201.13276 (2022)