Portolés Elías, Iwakiri Shuichi, Zheng Giulia, Rickhaus Peter, Taniguchi Takashi, Watanabe Kenji, Ihn Thomas, Ensslin Klaus, de Vries Folkert K
Solid State Physics Laboratory, ETH Zurich, Zurich, Switzerland.
International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan.
Nat Nanotechnol. 2022 Nov;17(11):1159-1164. doi: 10.1038/s41565-022-01222-0. Epub 2022 Oct 24.
Magic-angle twisted bilayer graphene (MATBG) hosts a number of correlated states of matter that can be tuned by electrostatic doping. Transport and scanning-probe experiments have shown evidence for band, correlated and Chern insulators along with superconductivity. This variety of in situ tunable states has allowed for the realization of tunable Josephson junctions. However, although phase-coherent phenomena have been measured, no control of the phase difference of the superconducting condensates has been demonstrated so far. Here we build on previous gate-defined junction realizations and form a superconducting quantum interference device (SQUID) in MATBG, where the superconducting phase difference is controlled through the magnetic field. We observe magneto-oscillations of the critical current, demonstrating long-range coherence of superconducting charge carriers with an effective charge of 2e. We tune to both asymmetric and symmetric SQUID configurations by electrostatically controlling the critical currents through the junctions. This tunability allows us to study the inductances in the device, finding values of up to 2 μH. Furthermore, we directly probe the current-phase relation of one of the junctions of the device. Our results show that complex devices in MATBG can be realized and used to reveal the properties of the material. We envision our findings, together with the established history of applications SQUIDs have, will foster the development of a wide range of devices such as phase-slip junctions or high kinetic inductance detectors.
魔角扭曲双层石墨烯（MATBG）存在许多可通过静电掺杂调节的关联物态。输运和扫描探针实验已证实了能带绝缘体、关联绝缘体和陈绝缘体以及超导性的存在。这种多种原位可调态使得可调谐约瑟夫森结得以实现。然而，尽管已经测量到了相位相干现象，但迄今为止尚未证明对超导凝聚体的相位差进行控制。在此，我们基于先前通过栅极定义的结的实现方式，在MATBG中形成了一个超导量子干涉器件（SQUID），其中超导相位差通过磁场进行控制。我们观察到临界电流的磁振荡，证明了有效电荷为2e的超导电荷载流子的长程相干性。我们通过静电控制通过结的临界电流，将其调谐到非对称和对称SQUID配置。这种可调谐性使我们能够研究器件中的电感，发现其值高达2 μH。此外，我们直接探测了器件中一个结的电流 - 相位关系。我们的结果表明，可以在MATBG中实现复杂器件并用于揭示材料的特性。我们设想，我们的发现与SQUID已有的应用历史相结合，将推动诸如相位滑移结或高动态电感探测器等各种器件的发展。
