Rotational symmetry breaking and nematicity in twisted graphene multilayers

Graphene-based moiré systems have attracted considerable interest in recent years as a remarkably versatile venue for a variety of correlated phenomena. In addition to insulating and superconducting phases, there is growing evidence that a number of rotationally faulted graphene multilayer systems, such as twisted bilayer and double-bilayer graphene, exhibit electronic nematic order: the spontaneous breaking of lattice rotation symmetry. In this talk I will present recent reports of rotation symmetry in twisted graphene multilayers, focusing in particular on twisted double-bilayer graphene (tDBG), and will discuss a comparison with theory. I will show that a combination of symmetry-based analysis and a microscopic continuum model provides an understanding of the structure of the nematic phase observed in tDBG. Furthermore, I will discuss experimental manifestations, such as a surprising tunability of the orientation of the nematic director. In broader sense, this talk aims to highlight graphene moiré materials as a compelling experimental venue for studying a new type of nematic order distinct from the conventional Ising nematic order.

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