Description
- Abstract:
- This thesis explores the interplay between broken symmetry and electronic correlations in emergent quantum phenomena within low-dimensional electron systems. The first half of the thesis centers on angle-resolved transport measurements, enabled by a novel planar sunflower geometry. We develop a new experimental protocol to systematically extract the tensorial parameters that characterize both the linear and nonlinear transport regimes. In Chapter 2, we investigate the moiré flat bands of magic-angle twisted trilayer graphene (TTG). By extracting the full conductivity matrix in the ohmic regime, we uncover an intimate link between nematicity, superconductivity, and strange metallicity, which enables a direct determination of the superconducting order parameter symmetry in TTG. We further demonstrate the capability to fully resolve the rank-3 nonlinear conductivity tensor using angle-resolved techniques. By measuring the potential distribution along the perimeter of the disk-shaped device, we provide experimental input to a comprehensive theoretical framework, allowing all nonlinear tensor components to be determined with exceptional precision. We apply this methodology to both TTG and Bernal bilayer graphene devices, and in the latter, report an unambiguous identification of the nonlinear Hall conductivity—the dissipationless component of second-order transport—alongside tensor components corresponding to dissipative nonlinear effects. Next, we explore excitons in the fractional quantum Hall effect in quantum Hall graphene bilayers. In the interlayer-coupled two component fractional quantum Hall regime, we observe two types of fractional excitons: one as a fractional analogue of the exciton condensate at total filling of one, and another involving fractionally charged constituents, obeying bosonic, fermionic, or anyonic statistics. In the decoupled limit, we showcase the identification and control of anyonic excitons in the Jain sequence via thermal excitation and electrostatic doping. Highlighting the rich landscape of this platform, we also demonstrate pseudospin-induced transitions and observe excitonic neutral modes at even-denominator states. Leveraging versatility of van der Waals heterostructures, we explore many-body, collective phenomena using both planar and vertical device architectures. Together, our findings offer key insights into correlated quantum phases in low-dimensional systems.
- Notes:
- Thesis (Ph. D.)--Brown University, 2025
Citation
Zhang, Naiyuan,
"Emergent Phenomena in Multilayer Graphene with Planar and Vertical Architectures"
(2025).
Physics Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.26300/4rqc-fx80
