Optical studies of quantum materials under high pressure
Dr. Xiang Li
Postdoctoral Research Associate
Division of Physics, Mathematics, and Astronomy
California Institute of Technology
The quantum nature of materials spans microscopic to macroscopic scales. This enables a wide array of physical properties that facilitate applications such as energy relevant technologies. The exotic properties arise from intertwined couplings of symmetry, topology, dimensionality and strong correlations, and are sensitive to external stimuli. We can use this sensitivity to unravel the complex interplay between the degrees of freedom by perturbing the interaction parameters and observing the corresponding responses. Pressure provides a clean and effective tunning parameter, but introduces challenges to successfully performing in situ measurements. In this talk, I will discuss how we employ two complementary optical techniques to probe the quantum physics of the strongly spin-orbit-coupled Mott insulator Sr 2 IrO 4 . We developed an ultralow frequency Raman system that permitted us to reveal a series of magnetic phases and their underlying spin-lattice correlations at pressures ranging from ambient to beyond 20 GPa. In addition, we used femtosecond pulse-probe measurements at high pressure and cryogenic temperatures to study the ultrafast dynamics. Taken together, these measurements give essential insight into the states of this 5d transition metal oxide, including the entry into a paramagnetic phase above 20 GPa that has some of the hallmarks of a quantum spin liquid. Finally, I will share our recent efforts to directly probe pressure-driven changes in symmetry by realizing a high-pressure rotational anisotropy second harmonic generation (RA-SHG) measurement on the Weyl semimetal TaAs. Taken together, these experiments open new windows into quantum materials by providing multiple probes for accessing and studying novel phases.
Hosted by Prof. Hsu
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