Synthesis and Strongly Correlated Physics of Two-Dimensional Quantum Materials

Abstract

Advancements in two-dimensional (2D) quantum materials have driven significant progress in various fields including electronic devices, optics, and quantum technologies. Among these, 2D transition metal dichalcogenides (TMDs) are especially intriguing due to their diverse quantum phases. Investigating these phases is essential for understanding fundamental quantum physics and developing future applications. In addition, exploring the interplay between these interesting states is highly desirable but remains challenging. In this thesis, we present our works on studying strongly correlated phases in 2D materials and developing new approaches to engineering quantum phases on demand within a single device.We first investigate monolayer tungsten ditelluride (WTe2), which exhibits multiple quantum phases, including the quantum spin Hall insulator (QSHI) and superconductor. We provide experimental evidence revealing the excitonic nature of its QSHI state, identifying monolayer WTe2 as the first topological excitonic insulator. This work establishes a material platform for future research into correlated insulators with nontrivial topology. Following our WTe¬2 studies, we discover another surprising phenomenon unique to 2D materials: a rapid, long-distance, non-Fickian mass transport of atomically thin metals on monolayer crystals at low temperatures. This process produces highly crystalline new 2D materials, further expanding the 2D material family. This discovery offers unique opportunities for engineering different phases within a single 2D device. Specifically, a class of non-superconducting 2D topological TMDs can be transformed into superconductors through this process. Moreover, the spatial interfaces between the original materials and the newly formed superconductors are atomically sharp and clean, providing a promising platform for studying the interplay between superconductivity and other intriguing phases intrinsic to 2D topological TMDs. As an example, we create superconducting junction in twisted bilayer MoTe2, which hosts fractional Chern insulator (FCI). The interplay between FCI and superconductivity could, in principle, realize new fractionalized electronic states that are important for creating topological qubits. In these junctions, we observe multiple anomalous superconducting behaviors contradicting conventional superconducting junctions. Our experiments not only revealed the rich quantum phases in 2D materials but also provide a novel route for creating a new class of quantum materials, enabling the investigation of intriguing physics at interfaces between distinct quantum phases.