Symmetry- and energy-resolved spectroscopy on complex materials

     There exists in nature a fascinating material class where the quantum-mechanical nature of electron-electron correlations manifests at a macroscopic level. Properties of these so called correlated materials result from the cooperative behavior of billions of interacting electrons ,and thus, are highly nontrivial and presents as a complex problem to solve. Striking consequences are known for certain material classes, which exhibit long-range orders that hold tremendous potential toward technological applications, but their mechanisms remain elusive. Examples include high-Tc superconductors, colossal magnetoresistance materials, and quantum spin liquids. A prerequisite for understanding these important quantum states is to elucidate their relation with competing phases within the material's phase diagram under various control parameters. This is particularly challenging provided the overwhelmingly rich behavior of these systems under external perturbations, and in fact, it is believed that a good number of phases still remain undetected, owing to the fact that they do not directly couple to conventional experimental probes.
  To overcome this challenge, we utilize a suite of table-top optical techniques to probe hidden orders of complex materials. By adopting creative designs of experimental configurations, we develop techniques ranging from symmetry-sensitive probes such as nonlinear harmonic generation polarimetry, Raman scattering, and magneto-optical Kerr rotation microscopy, to energy-sensitive probes such as broadband terahertz time-domain spectroscopy and whitelight spectroscopy. Together they form a multi-messenger probing system that provides well-rounded information on the charge, orbital, spin, and lattice degrees of freedom, which paves the way towards universal understandings of properties of complex materials.

 

Selected publications of our work in this area:

• Science 367, 285 (2020).

• Phys. Rev. Lett. 128, 187402 (2022).

• Phys. Rev. B 106, 014101 (2022).

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