2025 Theses Doctoral

Nano-optics and Nano-photocurrents in van der Waals Quantum Materials

Dong, Yinan

In this dissertation, we will use local and nonlocal detection of scanning nearfield signals to unravel emerging quantum phenomena in van der Waals quantum materials at nanoscale.

In Chapter 1, we will introduce the materials and methodologies for this dissertation. Two prototype van der Waals material systems, graphene and transition metal dichalcogenides (TMD) with their unconventional allotropes will be discussed. We will also introduce the measurable quantities and principles for using multi-messenger scanning nearfield optical microscopy to study van der Waals materials.

In Chapter 2 and 3, we will focus on nearfield light-matter interactions in monolayer graphene subject to DC currents. Specifically, we will discuss the discovery of Fizeau drag effect in graphene plasmonics in Chapter 2, and currrent-driven nonequilibrium effects probed by nano-optics and nano-photocurrents in Chapter 3.

In Chapter 4, we will reveal the flatband excitons in a three-dimensional super-twisted transition metal dichalcogenide, as well as its other unique properties.

In Chapter 5, we will discuss the quantum geometric photocurrents in crystalline multilayer graphene, with intrinsic domainless ferroelectricity probed by shift current.

In conclusion, with a series of original discoveries in graphene and TMD, this dissertation establishes nano-optics and nano-photocurrents as sensitive probes of the emerging quantum properties in van der Waals materials at a range of temperatures and energy scales.