Quantum geometry and chiral responses in van der Waals heterostructures

• Main Author: Arora, Arpit
• Other Authors: Justin Song Chien Wen
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Science::Physics
• Online Access: https://hdl.handle.net/10356/164059
• Institution: Nanyang Technological University

The rapid progress in the ability to fabricate van der Waals heterostructures in the past decade has enabled the synthesis of new systems with accessible control over electron wavefunction and correlation. The electronic states in these materials are fully exposed, and thus easily addressable which makes van der Waals heterostruc- tures a striking platform to explore quantum geometric effects. In this thesis, I study chiral responses related to quantum geometry in van der Waals heterostruc- tures with an aim to deepen the connection between quantum geometry, electron transport, nanophotonics and magnetism at the fundamental and applied levels. I exemplify this using three examples: edge magnetoresistance, helical photocurrents and non-reciprocal bulk plasmonics – which constitute three distinct parts of this thesis. In the first part, I describe how the bulk orbital texture modifies the edge wavefunc- tion and enables a large out of plane edge magnetoresponse in monolayer WTe2. This is determined by broken symmetries in the bulk and characterised by an un- usual anisotropic edge magnetoresistance. In the second part, I show that large circular injection currents in THz regime can manifest in strained twisted bilayer graphene heterostructures. These currents are gate tunable, and arise due to asym- metrically distributed and peaked interband Berry curvature dipole. This makes twisted bilayer graphene a promising material for THz technology. In the third part, I propose a new class of plasmons – quantum metric plasmons – which are in- trinsically non-reciprocal in the bulk. These plasmons arise due to quantum metric induced bulk directional currents in materials hosting stronger Coulomb interac- tions with broken parity and time reversal symmetries. I also discuss how quantum metric plasmons can manifest in twisted bilayer graphene heterostructures at 3/4 filling. The quantum geometry dependent chiral responses discussed in this thesis present new possibilities to control the intrinsic directional motion of electrons and their collective modes which can be harnessed in electronic quantum metamaterials and used for nanoscale device operation.