Department of Physics, Brown University, Providence, RI 02912, USA.
National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
Science. 2021 Mar 19;371(6535):1261-1265. doi: 10.1126/science.abb8754.
Controlling the strength of interactions is essential for studying quantum phenomena emerging in systems of correlated fermions. We introduce a device geometry whereby magic-angle twisted bilayer graphene is placed in close proximity to a Bernal bilayer graphene, separated by a 3-nanometer-thick barrier. By using charge screening from the Bernal bilayer, the strength of electron-electron Coulomb interaction within the twisted bilayer can be continuously tuned. Transport measurements show that tuning Coulomb screening has opposite effects on the insulating and superconducting states: As Coulomb interaction is weakened by screening, the insulating states become less robust, whereas the stability of superconductivity at the optimal doping is enhanced. The results provide important constraints on theoretical models for understanding the mechanism of superconductivity in magic-angle twisted bilayer graphene.
控制相互作用的强度对于研究关联费米子系统中出现的量子现象至关重要。我们引入了一种器件几何结构，其中魔角扭曲双层石墨烯被放置在伯纳尔双层石墨烯的附近，两者之间隔着一个 3 纳米厚的势垒。通过利用伯纳尔双层石墨烯的电荷屏蔽，扭曲双层石墨烯内的电子-电子库仑相互作用的强度可以连续调节。输运测量表明，调节库仑屏蔽对绝缘态和超导态有相反的影响：随着屏蔽削弱库仑相互作用，绝缘态变得不那么稳定，而在最佳掺杂下超导稳定性增强。这些结果为理解魔角扭曲双层石墨烯中超导机制的理论模型提供了重要的约束。
