Jang Seong, Park Geon-Hyoung, Park Sein, Jeong Hyeon-Woo, Watanabe Kenji, Taniguchi Takashi, Lee Gil-Ho
Department of Physics, Pohang University of Science and Technology, Pohang 37673, Republic of Korea.
Research Center for Functional Materials, National Institute for Materials Science, Tsukuba 305-0047, Japan.
Nano Lett. 2024 Dec 11;24(49):15582-15587. doi: 10.1021/acs.nanolett.4c03767. Epub 2024 Nov 28.
Graphene's exceptional electronic mobility, gate-tunability, and contact transparency with superconducting materials make it ideal for exploring the superconducting proximity effect. However, the work function difference between graphene and superconductors causes unavoidable doping of graphene near contacts, forming a p-n junction in the hole-doped regime and reducing the contact transparency. This challenges the device implementation that exploits graphene's bipolarity. To address this limitation, we developed a new fabrication scheme for two-dimensional superconducting contacts that allows independent control over charge concentration and polarity for both the graphene in contact with superconductors and the graphene channel. Contact transparency, conductance enhancement, and Josephson coupling were measured to confirm transparent contacts with both polarities of graphene. Moreover, we demonstrated the Andreev process in the quantum Hall edge state at a negative filling factor of ν = -2. This scheme will open up avenues for realizing various theoretical propositions using the bipolarity of graphene combined with superconductivity.
石墨烯卓越的电子迁移率、栅极可调性以及与超导材料的接触透明度，使其成为探索超导邻近效应的理想材料。然而，石墨烯与超导体之间的功函数差异会导致接触附近的石墨烯不可避免地出现掺杂，在空穴掺杂区域形成一个 p-n 结，并降低接触透明度。这对利用石墨烯双极性的器件实现构成了挑战。为解决这一限制，我们开发了一种用于二维超导接触的新制造方案，该方案能够对与超导体接触的石墨烯以及石墨烯通道的电荷浓度和极性进行独立控制。通过测量接触透明度、电导增强和约瑟夫森耦合，证实了与石墨烯两种极性的透明接触。此外，我们在 ν = -2 的负填充因子下的量子霍尔边缘态中展示了安德列夫过程。该方案将为利用石墨烯双极性与超导性相结合来实现各种理论命题开辟道路。
