Investigations into the Electronic States of 2D Quantum Material WTe2

Abstract

Quantum materials are those whose properties cannot be explained without invoking quantum mechanics. This broad class of materials includes superconductors, topological insulators, magnets, and Weyl semimetals. These materials are of great research interest to both better understand nature as well as to harness their unique properties for further technological development. With the successful isolation of graphene, the field of 2D materials was born. The restriction in dimension changes the physics of the electrons, in addition to allowing for increased control over the material properties using electrostatic gates, whose effectiveness is highly limited in 3D. This thesis focuses on the electronic properties of the 2D quantum material WTe2. Following a brief background on the history of WTe2, I will discuss our studies of the spin-axis of the edge states of monolayer WTe2, demonstrating the helical nature of these states and thus confirming that WTe2 is a 2D topological insulator. Next, I will report on our experiments to study the edge states at millikelvin temperatures, where the linear conductance of the edges freezes out. From there, I will report on new data from high-quality crystals grown from the so-called “horizontal flux” technique. I will show how WTe2 has a stronger superconducting state than previously reported, showing strong density dependence while having a critical temperature larger than 1.5 K. We also report unambiguous evidence of the presence of Shubnikov-de Haas oscillations in monolayer WTe2.