Electronic, Optical, and Thermal Probes of the Layered Mott Insulator α-RuCl3 in the Atomically Thin Limit
Date of Award
Doctor of Philosophy (PhD)
Alpha-ruthenium(III) chloride (α-RuCl3) is a layered Mott insulator and van der Waals material that can be cleaved down to a single atomic layer. This material is a promising candidate to realize the Kitaev quantum spin liquid, a strongly correlated phase of matter expected to host fractionalized quasiparticles and a potential platform for topological quantum computation. When α-RuCl3 is placed in direct contact with the layered semimetal graphene we observe a strong charge transfer between the two materials despite the electrically insulating nature of α-RuCl3, which absorbs ≈ 4 × 10^13 electrons/cm^2 from the graphene. Remarkably, this charge transfer persists and is even tunable by introducing an insulating barrier of varying thickness between the materials, resulting in a spatial separation of the transferred charge from its source analogous to modulation doping in epitaxially grown semiconductors. We can exploit this controllable charge transfer to create graphene devices with readily-patternable electric potential landscapes. Further, we can utilize electronic transport in graphene coupled to α-RuCl3 to explore the thermal properties of the latter which may reveal signatures of fractionalized quasiparticles. We present electronic transport, Raman spectroscopy, and first principles calculations for graphene/α-RuCl3 heterostructures to characterize the charge transfer between the two materials, both in perfect contact with each other and spatially separated by an insulating boundary. We then use electronic transport, scanning tunneling spectroscopy/microscopy, and first principles calculations to demonstrate an ultra-sharp lateral p-n junction defined by modulation-doping graphene with α-RuCl3. Next, we discuss anomalous electronic transport phenomena observed in graphene/α-RuCl3 heterostructures, including a temperature-dependent change in the charge transfer and an apparent screening of gate electric fields by the α-RuCl3. We discuss the possibility of an emergent charge-doping-driven ferromagnetic or ferroelectric phase transition as explanations for this behavior. Finally, we introduce microwave-frequency Johnson-Nyquist noise thermometry measurements in graphene/α-RuCl3 devices aimed at investigating the thermal properties of exfoliated α-RuCl3.
Chair and Committee
Balgley, Jesse, "Electronic, Optical, and Thermal Probes of the Layered Mott Insulator α-RuCl3 in the Atomically Thin Limit" (2022). Arts & Sciences Electronic Theses and Dissertations. 2668.