Quantum Hall Effect in Graphene/transition Metal Dichalcogenide Spin-orbit System PDF Download

Author: Dongying Wang (Ph. D. in physics)
Publisher:
ISBN:
Category : Graphene
Languages : en
Pages : 0

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Book Description
Van der Waals heterostructure based on stacking two dimensional materials gives rise to new possibilities for engineering multifunctional electronic and spintronic systems. While combining the merits of individual layers, heterostructures provide a platform for studying the interfacial interactions. In particular, significant effort has been made to increase the spin-orbit coupling in graphene by coupling it to transition metal dichalcogenides towards realizing topological electronic ground states. In this thesis, using quantum Hall measurements as a precise probe, we investigate the induced spin-orbit coupling (SOC) in graphene by the proximity to transition metal dichalcogenides (TMDCs) to achieve two main objectives: " Obtain signatures of an enhanced SOC in graphene by proximity to a semiconducting TMDC using quantum Hall measurements." Study the modification that SOC brings into the graphene quantum Hall system, together with other striking interactions, such as Coulomb interaction, exchange coupling and superconducting correlation, which would be building blocks for engineering a graphene-based multifunctional system. To achieve such objectives, many efforts have been devoted to fabricating carefully designed samples, adapting and proposing experimental protocols based on quantum Hall measurements, and in the analysis and modeling of the signals. This thesis is organized as following: Chapter 1 briefly introduces the background of graphene and proximity induced SOC in graphene/TMDCs heterostructure and quantum Hall effect. In Chapter 2, we present the main experimental method of device fabrication and characterization. Here, we will talk about the process of fabricating graphene/TMDCs van der Waals heterostructure with ultra-clean interface, and further introduce some basic idea in electrical transport measurements. In Chapter 3, we demonstrate enhanced SOC in bilayer graphene on WSe2 by quantum Hall measurements. We will show distinct Landau level crossing pattern in this system under a tunable displacement field over a wide range of carrier density. Within the single particle model, we isolate and quantify the Ising SOC and Rashba SOC strength and further bring up the effects of Coulomb interaction. To further study the interplay of Coulomb interaction with induced SOC in the quantum Hall system, we study a monolayer graphene on WSe2 system with in a Hartree- Fock model. In Chapter 4, we show the experimental details and theoretical analysis. The effective dielectric constant as well as the SOC parameters are extracted based on the model, showing consistency with previous work. In addition, a canted anti-ferromagnetic state to ferromagnetic state phase transition at n = 0 LL takes place at low field thanks to the presence of SOC. In Chapter 5, we move one more step forward by bringing exchange coupling into the spin-orbit system, towards realizing helical edge states. The introduction of Cr2Ge2Te6 enable us to directly probe the energy spectrum. We observe clear modifications in graphene's Landau level structure caused by proximity-induced spin- orbit coupling and exchange coupling, which are qualitatively in agreement with the single particle model. In addition, we also show our efforts towards topological superconducting states by introducing superconducting correlation in the graphene/TMDCs system. Premilitary results and proposals of further experiments are shown in Appendix D