2026 Theses Doctoral

Imaging Multi-Particle Correlations with Time-Resolved Nonlinear Microscopy

Tulyagankhodjaev, Jakhangirkhodja

Establishing control over electronic dynamics in next-generation semiconductors requires understanding and controlling interactions between different degrees of freedom, including electron-phonon and the electron-electron interactions.

The first part of this thesis explores how novel forms of electron-phonon interactions hosted by structurally hierarchical semiconductors can mediate new forms of macroscopic, wavelike electronic energy transport regimes at room temperature, overcoming scattering losses that plague every semiconductor technology. The second part of the thesis reports on the development of a new precision spectro-microscopy tool to interrogate multi-particle dynamics such as electron-electron interactions with high spatiotemporal resolution.

In Chapter 3, we leverage strong electron-phonon interactions in the superatomic semiconductor Re₆Se₈Cl₂, demonstrating the formation of acoustic exciton-polarons, a particle carrying electronic energy that is shielded from scattering with lattice phonons. Using stroboscopic scattering microscopy (stroboSCAT), we directly image quasi-ballistic exciton motion with mean-free-paths of up to a micrometer and lifetimes of several nanoseconds. Using transient reflection spectroscopy, we observe how the initial exciton is spontaneously stabilized by the lattice.

In Chapter 4, we propose that this stabilization is driven by a unique combination of flat electronic bands and strong deformation potential, evidenced by temperature-dependent transport measurements. The unique energy-momentum dispersion relation of acoustic polarons creates a narrow momentum distribution that limits single-phonon scattering, enabling propagation of excitons in Re₆Se₈Cl₂ faster than charge carriers in silicon. We also report on the measurement of the polaron’s size using power-dependent transient reflection spectroscopy.

Chapter 5 details our efforts to generalize this phenomenon to other superatomic semiconductors by attempting to resolve the origin of different transport domains in Re₆Se₈Cl₂. Overall, we believe that the novel electron-phonon interactions discovered in Re₆Se₈Cl₂ enable unconventional strategies for exceptional electronic transport and open a pathway for high-temperature coherence and dissipation-free electronic propagation in semiconductors.

Establishing control over electronic states requires new techniques to resolve many-body dynamics. In Chapter 6, we detail the adaptation of a new spectroscopic concept called intensity-cycling to the spatiotemporal domain. Spatiotemporal optical microscopies, including stroboSCAT, have provided key functional metrics into the transport dynamics of a diverse set of energy carriers. However, these techniques cannot distinguish single-particle from multi-particle states, limiting the ability to resolve multi-particle correlations we aim to exploit for next generation, scatter-free technologies. Intensity-cycling solves this problem for transient absorption spectroscopy. We extend this technique to transient scattering microscopy, enabling significant improvements in the signal-to-noise ratio of single-particle states, imaging spatiotemporal evolution of exciton-exciton annihilation, mapping of dielectric disorder, and imaging the dynamics of a polaron Mott Transition. This chapter develops a new precision tool to image how many-body states shape material function.