BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Talks.cam//talks.cam.ac.uk// X-WR-CALNAME:Talks.cam BEGIN:VEVENT SUMMARY: A Spiral Twist to the "\;Normal"\; State of Magic-Angle B ilayer Graphene - Siddharth Parameswaran (University of Oxford) DTSTART:20221013T130000Z DTEND:20221013T140000Z UID:TALK178070@talks.cam.ac.uk CONTACT:Jan Behrends DESCRIPTION:Intense experimental efforts have uncovered a wide range of in teraction-driven phenomena in magic-angle twisted bilayer graphene (TBG)\, including the observation of quantised topological responses\, correlated insulating states\, and most famously\, gate-tunable superconductivity. T hese phenomena challenge a weak-coupling treatment yet the strong-coupling limit\, despite admitting an elegant hidden symmetry structure (which I w ill review)\, is also in tension with experiments: for instance\, it fails to fully explain the sequence of insulating and semimetallic states at co mmensurate fillings and their associated Landau fan diagrams. In this talk \, I will argue that even very small strain (ubiquitous in experimental sa mples) drives the system to an intermediate coupling regime\, where the no rmal-state phase diagram is dominated by a novel translation symmetry-brea king order dubbed the incommensurate Kekulé spiral (IKS). This order mani fests as a Kekulé distortion on the microscopic graphene scale whose phas e rotates on the moiré scale: its existence hence relies essentially on t he multiscale nature of moiré materials. I will describe the properties a nd origin of the IKS state and its link to the 'strong coupling' phases of TBG. I will demonstrate that these findings are broadly consistent with e xtant experimental observations in TBG and comment on its implications for the origin of superconductivity in graphene moiré bilayers.\n\nThis talk is based on Phys. Rev. X 11\, 041063 (2021) and Phys. Rev. Lett. 128\,156 401 (2022). LOCATION:TCM Seminar Room END:VEVENT END:VCALENDAR