Tunable strongly coupled superconductivity in magic-angle twisted trilayer graphene
Tunable strongly coupled superconductivity in magic-angle twisted trilayer graphene
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DOI：
10.1038/s41586-021-03192-0
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发表时间：
2021-02-01
期刊：
影响因子：
64.8
通讯作者：
Jarillo-Herrero, Pablo
中科院分区：
文献类型：
--
作者：
Park, Jeong Min;Cao, Yuan;Jarillo-Herrero, Pablo
莫尔超晶格(1,2) 最近已成为一个平台，可以在该平台上以前所未有的可调性来研究相关物理和超导性(3-6)。尽管在其他几种莫尔系统中也观察到了相关效应(7-17)，但魔角扭曲双层石墨烯仍然是唯一一种可重复测量鲁棒超导性的系统(4-6)。在这里，我们在魔角扭曲三层石墨烯（MATTG）（18）中实现了莫尔超导体，其电子结构和超导性能比魔角扭曲双层石墨烯具有更好的可调性。作为密度和电场函数的霍尔效应和量子振荡的测量使我们能够确定正常金属状态下系统的可调相边界。零磁场电阻率测量表明，超导性的存在与每个莫尔晶胞两个载流子出现的对称破缺相位密切相关。我们发现超导相在部分围绕对称破缺相的范霍夫奇点处受到抑制和限制，这很难与弱耦合巴丁-库珀-施里弗理论相一致。此外，我们的系统广泛的原位可调谐性使我们能够达到超强耦合状态，其特征是达到平均粒子间距离的Ginzburg-Landau相干长度和超过0.1的非常大的T-BKT/F值（其中T-BKT和T-F分别是Berezinskii-Kosterlitz-Thouless转变和费米温度）。这些观察结果表明，MATTG 可以电调谐到接近二维玻色-爱因斯坦凝聚态的交叉点。我们的研究结果建立了一系列可调谐莫尔超导体，它们有可能彻底改变我们对强耦合超导的基本理解和应用。
Moire superlattices(1,2) have recently emerged as a platform upon which correlated physics and superconductivity can be studied with unprecedented tunability(3-6). Although correlated effects have been observed in several other moire system(7-17), magic-angle twisted bilayergraphene remains the only one in which robust superconductivity has been reproducibly measured(4-6). Here we realize a moire superconductor in magic-angle twisted trilayer graphene (MATTG)(18), which has better tunability of its electronic structure and superconducting properties than magic-angle twisted bilayer graphene. Measurements ofthe Hall effect and quantum oscillations as a function of density and electric field enable us to determine the tunable phase boundaries of the system in the normal metallic state. Zero-magnetic-field resistivity measurements reveal that the existence of superconductivity is intimately connected to the broken-symmetry phase that emerges from two carriers per moire unit cell. We find that the superconducting phase is suppressed and bounded at the Van Hove singularities that partially surround the broken-symmetry phase, which is difficult to reconcile with weak-coupling Bardeen-Cooper-Schrieffer theory. Moreover, the extensive in situ tunability of our system allows us to reach the ultrastrong-coupling regime, characterized by a Ginzburg-Landau coherence length that reaches the average inter-particle distance, and very large T-BKT/F, values, in excess of 0.1 (where T-BKT and T-F are the Berezinskii-Kosterlitz-Thouless transition and Fermi temperatures, respectively). These observations suggest that MATTG can be electrically tuned close to the crossover to a two-dimensional Bose-Einstein condensate. Our results establish a family of tunable moire superconductors that have the potential to revolutionize our fundamental understanding of and the applications for strongly coupled superconductivity.