Since the discovery of the quantum Hall effect, novel states of matter—characterized by phenomena such as fractional charge and anyonic excitations—have reshaped our understanding of two-dimensional electronic transport. Yet, no single experimental approach can fully capture the dual particle- and wave-like nature of these exotic quasiparticles. While shot-noise measurements have shed light on their particle aspects, interferometric techniques are indispensable for probing their wave properties and potential non-Abelian statistics.
This thesis advances quantum Hall interferometry in graphene, a platform renowned for its long coherence lengths, into the fractional regime. Building on earlier Mach–Zehnder interferometry at integer filling factors, we developed a nanofabrication scheme based on patterned graphite gates, combined with edge-contact engineering via silicon back-gate doping. This architecture enabled the first observation of interference at filling factor ν = 2/3. From these measurements, we extracted the spin polarization and edge structure of the fractional state and studied its decoherence mechanisms under varying temperature and DC bias.
In the integer regime, we demonstrated spin degeneracy breaking between copropagating edge channels and uncovered quantum eraser-like behavior: the coherence of one interferometer could be suppressed by measurements performed on the other. A novel device geometry further allowed independent access to inner and outer edge channels, revealing their mutual dephasing and distinct interference responses under bias.
Finally, in the ferromagnetic quantum Hall regime at ν = 1, we explored magnon emission and diffraction. By tuning a downstream region to ν = 1+ϵ, we entered a regime suggestive of skyrmion formation, as evidenced by directional modifications of spin-wave propagation. This led to the realization of a magnon diffraction experiment, providing new insights into the spin textures of interacting edge states in graphene