Colloquium: Dr. Dacen Waters | University of Washington
In-Person PHYS 401
Location
Physics : 401
Date & Time
February 12, 2024, 11:00 am – 12:00 pm
Description
TITLE: "A new twist on graphite: correlated, topological, and “mixed-dimensional” physics in moiré systems”
ABSTRACT: Programmable quantum materials are key for the development of useful electronic devices, ranging from the silicon transistor widely implemented today to the future of quantum computing. Bulk graphite has generally not been considered a particularly promising material for such devices, despite its natural abundance, given that it is generally not programmable: e.g. it has no electronic band gap, is non-magnetic, and does not superconduct. However, the novel tuning knob of twist angle has emerged as a powerful tool for engineering exciting phenomena in two dimensional (2D) van der Waals material. A twist angle introduced between 2D materials creates a long wavelength moiré pattern from which new properties can emerge that do not exist in the parent material, most famously in the case of superconductivity in magic-angle twisted bilayer graphene. In this work, I will show that controllably introducing a single twisted interface in multilayer graphene radically changes its properties and turns it into a highly tunable material platform. I will present systematic quantum transport studies of twisted M+N graphitic thin film devices, where M-layers of graphene are twisted with respect to N-layers. I will show the commonalities across different layer number combinations and explore the surprising differences that lead to exciting new properties. In the atomically thin limit, an abundance of symmetry broken correlated states and topological phases emerge, owing to a localization of the density of states at the twisted interface. As the number of layers is increased towards the bulk limit, localized moiré surface states interact with and modify bulk graphitic states, creating a novel 2D-3D hybrid system and establishing a new class of “mixed-dimensional” moiré materials. These results demonstrate the powerful capabilities of moiré tuning and the potential for utilizing moiré systems for designer quantum devices. Further, the understanding of twisted graphene multilayer systems likely generalizes to other material platforms, potentially providing new control knobs for the plethora of exciting phases of matter that continue to emerge in moiré materials.
ABSTRACT: Programmable quantum materials are key for the development of useful electronic devices, ranging from the silicon transistor widely implemented today to the future of quantum computing. Bulk graphite has generally not been considered a particularly promising material for such devices, despite its natural abundance, given that it is generally not programmable: e.g. it has no electronic band gap, is non-magnetic, and does not superconduct. However, the novel tuning knob of twist angle has emerged as a powerful tool for engineering exciting phenomena in two dimensional (2D) van der Waals material. A twist angle introduced between 2D materials creates a long wavelength moiré pattern from which new properties can emerge that do not exist in the parent material, most famously in the case of superconductivity in magic-angle twisted bilayer graphene. In this work, I will show that controllably introducing a single twisted interface in multilayer graphene radically changes its properties and turns it into a highly tunable material platform. I will present systematic quantum transport studies of twisted M+N graphitic thin film devices, where M-layers of graphene are twisted with respect to N-layers. I will show the commonalities across different layer number combinations and explore the surprising differences that lead to exciting new properties. In the atomically thin limit, an abundance of symmetry broken correlated states and topological phases emerge, owing to a localization of the density of states at the twisted interface. As the number of layers is increased towards the bulk limit, localized moiré surface states interact with and modify bulk graphitic states, creating a novel 2D-3D hybrid system and establishing a new class of “mixed-dimensional” moiré materials. These results demonstrate the powerful capabilities of moiré tuning and the potential for utilizing moiré systems for designer quantum devices. Further, the understanding of twisted graphene multilayer systems likely generalizes to other material platforms, potentially providing new control knobs for the plethora of exciting phases of matter that continue to emerge in moiré materials.
