Dutta Ranit, Ghosh Ayan, Mandal Shinjan, Watanabe Kenji, Taniguchi Takashi, Krishnamurthy H R, Banerjee Sumilan, Jain Manish, Das Anindya
Department of Physics, Indian Institute of Science, Bangalore 560012, India.
Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
ACS Nano. 2025 Feb 11;19(5):5353-5362. doi: 10.1021/acsnano.4c12770. Epub 2025 Feb 3.
Superconductivity (SC) in twisted bilayer graphene (tBLG) has been explored by varying carrier concentrations, twist angles, and screening strength, with the aim of uncovering its origin and possible connections to strong electronic correlations in narrow bands and various resulting broken symmetries. However, the link between the tBLG band structure and the onset of SC and other orders largely remains unclear. In this study, we address this crucial gap by examining in situ band structure tuning of a near magic-angle (θ ≈ 0.95°) tBLG device with a displacement field () and reveal competition between SC and other broken symmetries. At zero , the device exhibits superconducting signatures without the resistance peak at half-filling, a characteristic signature with a strong electronic correlation. As increases, the SC is suppressed, accompanied by the appearance of a resistance peak at half-filling. Hall density measurements reveal that at zero , SC arises around the van Hove singularity (vHs) from an isospin or spin-valley unpolarized band. At higher , the suppression of SC coincides with broken isospin symmetry near half-filling with lifted degeneracy ( ∼ 2). Additionally, as the SC phase becomes weaker with , vHs shifts to higher fillings, highlighting the modification of the underlying band structure with the applied electric field. These findings, with recent theoretical study on SC in tBLG, highlight the competition, rather than being connected concomitantly, between SC and other orders promoted by broken symmetries.
通过改变载流子浓度、扭转角和屏蔽强度，人们对扭曲双层石墨烯（tBLG）中的超导性（SC）进行了探索，目的是揭示其起源以及与窄带中强电子关联和各种由此产生的对称性破缺之间的可能联系。然而，tBLG能带结构与超导及其他有序态的起始之间的联系在很大程度上仍不明确。在本研究中，我们通过使用位移场（）对近魔角（θ≈0.95°）的tBLG器件进行原位能带结构调谐来填补这一关键空白，并揭示超导与其他对称性破缺之间的竞争。在 = 0时，该器件表现出超导特征，在半填充时没有电阻峰，这是强电子关联的一个特征标志。随着 的增加，超导被抑制，同时在半填充时出现电阻峰。霍尔密度测量表明，在 = 0时，超导在范霍夫奇点（vHs）附近由同位旋或自旋谷非极化能带产生。在较高的 时，超导的抑制与半填充附近同位旋对称性破缺以及简并度提升（ ∼ 2）相吻合。此外，随着超导相随着 变弱，vHs向更高的填充移动，突出了外加电场对底层能带结构的改变。这些发现与最近关于tBLG中超导的理论研究一起，突出了超导与由对称性破缺促进的其他有序态之间的竞争，而不是同时存在的联系。
