Proximity and Strain Driven Quantum Transport in Graphene

Abstract

Graphene, with its relativistic band structure and high mobility, provides a promising ground for exploring emergent electronic phenomena when interfaced with other two-dimensional materials. By introducing symmetry-breaking perturbations such as interfacial strain, displacement fields, or proximity-induced magnetism, the pristine band structure of graphene can be engineered to exhibit a wide variety of transport phenomena. This research presents a comprehensive study of such effects, revealing how symmetry, band geometry, and proximity-induced effects combine to produce novel Hall and magnetoresistance responses in graphene-based systems. In the first part of the thesis, we investigate a time-reversal symmetric Hall effect in high-mobility graphene/WSe2 heterostructures. This unconventional linear Hall response is observed up to room temperature and is tunable via an external perpendicular electric field. Through combined experimental and theoretical analysis, we attribute the effect to strain-induced inversion symmetry breaking and anisotropic band dispersion resulting from lattice mismatch between graphene and WSe2. These results establish a new class of Hall transport driven by spatial symmetry breaking. The second part of the work deals with the observation of giant odd-parity magnetoresistance (OMR) in bilayer graphene interfaced with the magnetic insulator Cr2Ge2Te6(CGT). We attribute the OMR to the interaction of the Berry curvature and orbital magnetic moment with an external magnetic field. This work demonstrates the potential of magneto transport as a probe of Berry curvature-related phenomena, especially in systems where anomalous Hall signals are masked by disorder. In the final part of the thesis, we demonstrate strain-induced pseudomagnetic fields in pristine single-layer graphene through low-field quantum oscillation measurements. Our observation of beating patterns in the quantum oscillation, attributed to valley polarization, provides the first transport-based signature of pseudo-magnetic fields in graphene. Moreover, we find that these quantum interference effects are tunable with a perpendicular electric displacement field, offering a method to manipulate valley-dependent phenomena in graphene.