Dynamical Control of Many-Body Interactions in Driven Quantum Matter

Author: Yang, Christopher Kai-Chen

Year: 2025

Degree: Dissertation (Ph.D.)

Advisor: Refael, Gil

Committee Members: Hsieh, David; Refael, Gil; Alicea, Jason F.; Motrunich, Olexei I.

Option: Physics

DOI: 10.7907/fh52-tw61

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.

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