Superfluid stiffness of twisted trilayer graphene superconductors

• 成果类型: Article
• 署名作者: Banerjee, Abhishek; Hao, Zeyu; Kreidel, Mary; Ledwith, Patrick; Phinney, Isabelle; Park, Jeong Min; Zimmerman, Andrew; Wesson, Marie E.; Watanabe, Kenji; Taniguchi, Takashi; Westervelt, Robert M.; Yacoby, Amir; Jarillo-Herrero, Pablo; Volkov, Pavel A.; Vishwanath, Ashvin; Fong, Kin Chung; Kim, Philip
• 署名单位: Harvard University; Massachusetts Institute of Technology (MIT); National Institute for Materials Science; National Institute for Materials Science; University of Connecticut
• 刊物名称: Nature
• ISSN/ISSBN: 0028-2473
• DOI: 10.1038/s41586-024-08444-3
• 发表日期: 2025-02-06
• 关键词: unconventional superconductivity; phase fluctuations; temperature; density; dependence; yba2cu3o6.95; disorder; lambda; state

摘要

The robustness of the macroscopic quantum nature of a superconductor can be characterized by the superfluid stiffness, rho s, a quantity that describes the energy required to vary the phase of the macroscopic quantum wavefunction. In unconventional superconductors, such as cuprates, the low-temperature behaviour of rho s markedly differs from that of conventional superconductors owing to quasiparticle excitations from gapless points (nodes) in momentum space. Intensive research on the recently discovered magic-angle twisted graphene family has revealed, in addition to superconducting states, strongly correlated electronic states associated with spontaneously broken symmetries, inviting the study of rho s to uncover the potentially unconventional nature of its superconductivity. Here we report the measurement of rho s in magic-angle twisted trilayer graphene (TTG), revealing unconventional nodal-gap superconductivity. Utilizing radio-frequency reflectometry techniques to measure the kinetic inductive response of superconducting TTG coupled to a microwave resonator, we find a linear temperature dependence of rho s at low temperatures and nonlinear Meissner effects in the current-bias dependence, both indicating nodal structures in the superconducting order parameter. Furthermore, the doping dependence shows a linear correlation between the zero-temperature rho s and the superconducting transition temperature Tc, reminiscent of Uemura's relation in cuprates, suggesting phase-coherence-limited superconductivity. Our results provide strong evidence for nodal superconductivity in TTG and put strong constraints on the mechanisms of these graphene-based superconductors.