Research

Efficient energy conversion and transport among electron, spin, and lattice dynamics are crucial for modern devices like computers, solar panels, and batteries. The interplay of electron and spin dynamics with lattice vibrations (phonons) causes charge trapping, energy dissipation, and spin relaxation, limiting device efficiency. To improve these technologies, real-time, atomically resolved visualization of these coupled motions is essential. Our research group uses advanced optical, Raman, and x-ray spectroscopic tools, including experiments at large-scale facilities like free-electron lasers and synchrotrons, to study how local electronic structures and spin states interact with lattice motions. This understanding is critical for designing materials that enhance charge transport, energy transfer, and information processing.  

Our multidisciplinary program involves collaborations across theory, materials science, chemistry, physics, non-linear optics, and spectroscopy, aiming to answer key questions and advance the development of more efficient materials and devices. 

Efficient Electron and Energy Transport in Materials

Directly observing phonon motions during carrier localization with local electronic structural sensitivity is crucial for understanding the interdependencies between phononic and electronic transport. This insight is essential for developing design principles to create efficient energy-harvesting materials. Electron-phonon interaction plays a vital role in controlling light conversion efficiency in various energy-harvesting materials. Our research focuses on understanding this fundamental process in semiconductors, thermoelectric materials, and 2D materials. By gaining a deeper understanding of these interactions, we aim to achieve design-specific control over these materials to enhance their energy-harvesting capabilities. Such an approach promises to improve the performance of solar cells, thermoelectric devices, and next-generation electronic materials, with greater efficiency.

Advancements in Data Storage and Processing

The rapid growth of data-driven technologies necessitates breakthroughs in data storage and processing technologies, as current approaches will soon be inadequate. Innovations like qubits and high-speed, energy-efficient, optically switchable magnetic memory devices promise a ~6 orders of magnitude improvement by reducing energy use from picojoules to attojoules per bit and speeding up processing times from nanoseconds to picoseconds/femtoseconds. However, these materials' efficiency is hindered by complex energy dissipation mechanisms involving electron-spin-lattice interactions. Our research aims to achieve a detailed understanding of these mechanisms to better control spin properties in magnetic memory devices and molecular qubits using targeted optical pulses, enhancing their performance in future technologies.

Non-equilibrium Dynamics of Quantum Materials

Advancements in quantum materials and ultrafast metrology have enabled new functionalities and optical/electronic responses. Novel materials exhibit unique properties like nontrivial band topology and strong-field interactions, while ultrafast techniques using attosecond and femtosecond pulses offer unprecedented control over electronic responses and reveal new quantum phenomena.  Optical control of topological materials is an emerging goal of condensed matter physics due to their robustness and applications in quantum technologies. Our research aims to develop an all-optical platform to probe and manipulate electron, spin, and nuclear degrees of freedom in quantum materials, enabling control of quantum matter towards a desired state using light. This will enhance the understanding of non-equilibrium dynamics, discover novel photoinduced phases, and explore new functionalities.

Method Development and Instrumentation

Advancing spectroscopic techniques is crucial for revealing novel excited state phenomena and gaining detailed insights into electron, spin, and nuclear dynamics at the atomic level with femtosecond to attosecond time resolution. To tackle this significant experimental challenge and address the important scientific questions outlined above, a key aspect of our research program is pushing the limits of existing spectroscopic methods. We employ novel soft X-ray light sources that utilize high-harmonic generation phenomena. The core-hole specificity of X-ray absorption provides information about the atom, spin state, and geometric environment-specific electronic structure. Additionally, ultrashort X-ray pulses produced via high-harmonic generation (HHG) enable time-resolved observations of coupled electron, spin, and lattice motions on their natural time scales, ranging from femtoseconds to attoseconds.