Abstract

The unusual properties of superconductivity in magic-angle twisted bilayer graphene (MATBG) have sparked enormous research interest. However, despite the dedication of intensive experimental efforts and the proposal of several possible pairing mechanisms, the origin of its superconductivity remains elusive. In this talk, using angle-resolved photoemission spectroscopy with micrometer spatial resolution, we show our observation on the replicas of the flat bands in superconducting MATBG unaligned with its hexagonal boron nitride (hBN) substrate, which are absent in non-superconducting MATBG aligned with the hBN substrate. Remarkably, the replicas are evenly spaced in energy, separated by 150 ± 15 meV, signaling the strong coupling of electrons in MATBG to a bosonic mode of this energy. By comparing our observations to simulations, the formation of replicas is attributed to the presence of strong inter-valley electron-phonon coupling to a K-point phonon mode. In total, the observation of these replica flat bands and the corresponding phonon mode in MATBG could provide important information for understanding the origin and the unusual properties of its superconducting phase [asdf].

Biography

Yulin received his B.S. from the University of Science & Technology of China in 2000 and Ph.D. in Physics from Stanford University in 2008. After working at SLAC National Accelerator Laboratory briefly (2008-2011, postdoc/associate staff scientist/ staff scientist), he joined the University of Oxford since 2012 as a Fellow of the Jesus College and university lecturer/associate professor/professor till now. Yulin is also an adjunct professor in Tsinghua University during 2014~2023 and ShanghaiTech University since 2014. 

Yulin’s research focuses on understanding the behavior of electrons in unconventional materials, including topological quantum materials, strongly correlated electron systems, and other functional materials. He is also dedicated to developing advanced instrumentation with novel capabilities to push the frontiers of current research. In recognition of his contributions to the field of topological quantum materials, Yulin has received several prestigious awards, including the William E. and Diane M. Spicer Young Investigator Award (2009), the OCPA Outstanding Young Researcher Award (2012), the Nakamura Lecture Award (2017), and the Kai Siegbahn Prize (2021). He is also recognized as a Highly Cited Researcher by the Web of Science.