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Strong coupling theory of superconductivity and flavor ordering in twisted bi (& tri) layer graphene

Date and Time: Tuesday, March 30, 2021, 01:30pm -
Location: Zoom

Speaker: Ashvin Vishwanath (Harvard University)

Moiré materials have emerged as highly tunable electronic systems that display a wide array of exotic phenomena. The simplest Moiré material is twisted bilayer graphene (TBG) consisting of two graphene sheets twisted by a small angle relative to each other. I will describe a simple toy model that captures the essential physics, that relates TBG to a pair of time-reversed quantum Hall systems with multiple flavors. This model explains the appearance of correlated insulators seen in recent experiments and predicts the nature of their collective excitations. The model also suggests a new topological mechanism for strong-coupling superconductivity that is distinct both from earlier weak coupling mechanisms as well as strong coupling theories proposed in other unconventional superconductors such as cuprates. This mechanism not only provides insights into the essential ingredients of superconductivity in TBG, it also helps explain why several other platforms are unlikely to host superconductors. Finally, I will explain how insights gained from this model have led to the discovery of a new Moiré superconductor, twisted trilayer graphene, and how they can be used to predict new platforms for unconventional superconductivity and other exotic phases.

Host:  Piers Coleman

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