"Multidimensional Spectroscopy of Quantum Materials"
Quantum materials, systems in which quantum effects lead to unique macroscopic phenomena with tremendous technological potential, comprise the forefront of condensed matter physics research. However, many vital aspects of their physics, such as disorder and coupling between degrees of freedom, are difficult to study using conventional experimental techniques.
In my talk today I will introduce a technique called 2-D spectroscopy, an optical analogue of NMR spectroscopy, that addresses these challenges. In the first part of my talk, we apply 2-D spectroscopy in the terahertz frequency range, in which collective excitations of quantum materials are typically found. We apply 2-D terahertz spectroscopy to the Josephson plasma resonance in La2-xSrxCuO4, a layered high-temperature superconductor, to distill the underlying plasmon correlations and reveal a disordered superconducting state [1]. In the second part of my talk, we apply 2-D spectroscopy in the optical frequency range to study exciton-polaritons in a semiconductor microcavity. By performing 2-D optical spectroscopy with a micrometer excitation spot size, we are able to target optical nonlinearities of specific exciton-polariton wavefunctions and realize nonlocal coupling between different exciton-polariton states that is coherent and quantum in nature.
[1] A. Liu et al., Nat. Phys. 20, 1751-1756 (2024)
[2] A. Liu et al., arXiV:2504.13830 (2025)
