Dynamical Control of Many-Body Interactions in Driven Quantum Matter

Citation

Yang, Christopher Kai-Chen (2025) Dynamical Control of Many-Body Interactions in Driven Quantum Matter. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/fh52-tw61. https://resolver.caltech.edu/CaltechTHESIS:04112025-180844471

Abstract

Strongly driven Floquet systems have emerged as promising platforms for exotic non-equilibrium physics, but their instability to heating motivates practical questions about how Floquet engineering can be useful. Although drive-induced heating is often attributed to interactions, this thesis adopts a different perspective, identifying regimes where dissipative many-body dynamics can stabilize Floquet physics and define remarkable new drive-tunable properties. This principle enables highly tunable many-body steady states with minimal heating, leading to a novel regime where drive control over single-particle Floquet states can extend to many-body interactions. Our theoretical and experimental results in Parts II and III center around two themes. The first theme focuses on discovering controllable and stable many-body Floquet states. The second explores further into what the future holds--envisioning the prospects for unconventional Floquet physics with nontraditional driving fields and three-dimensional materials.

Part II of this thesis leverages kinematic constraints on low-dimensional many-body scattering as new principles for tuning and stabilizing Floquet phases. First, we predict that a circularly polarized laser can drive slow electrons of moiré systems into a subsonic regime where they decouple from the intrinsic 2D acoustic phonons of the system. This "slow-electron regime" enables optical control over the steady-state occupation of topological Floquet states and the resulting anomalous Hall conductivity. Second, we present experimental transport signatures of steady Floquet physics in graphene irradiated by a continuous-wave laser. Our experiment, performed at 3-4 K lattice temperatures with lasers off-resonant to optical phonons, creates electron-phonon scattering bottlenecks that stabilize persistent low-temperature phases with light-induced longitudinal transport characteristics. The long-lived many-body phase represents the first experimental signatures of steady Floquet physics in a metallic solid.

Part III presents emerging opportunities for many-body Floquet engineering beyond traditional optically-driven, low-dimensional materials. We first explore beyond-optical driving fields, revealing the emergence of quantized charge transport in 1D systems driven by coherent phonons. Incoherent phonons relax electrons into a topological spatiotemporal Floquet state with quantized group velocity set by the coherent phonon, realizing topological charge pumping in a highly non-adiabatic setting. Finally, we address the topological effects of time-periodic drives beyond low-dimensional systems, revealing that THz-frequency, circularly polarized light can induce topological chiral plasmons in Weyl semimetals with band anisotropy, broken time-reversal symmetry, and broken inversion symmetry.

The theoretical and experimental work in this thesis represent key progress towards realizing persistent Floquet physics for diverse applications in quantum device engineering.

Thesis Files