Development of Optical Techniques for Probing Quantum Materials

Quantum materials are a growing field of interest in condensed matter physics and materials science due to their manifestation of quantum mechanical effects on the macroscale. Interactions between the charge, spin, lattice, and orbital degrees of freedom, combined with topology and often reduced dimensionality lead to the emergence of electronic ground states which defy understanding in terms of classical physics. Within the field of quantum materials, particular interest is placed on unconventional superconductors as possible candidates for use in quantum information science. Considerable inquiry is focused on the pairing mechanism in unconventional superconductors, as well as interplay between superconducting states and adjacent low-temperature states such as charge density wave (CDW) order and ferroelectricity. This thesis focuses on optical characterization of the quantum materials SrTiO3 and CsV3Sb5, both unconventional superconductors. I will discuss the methods used to characterize these materials: second harmonic generation (SHG) and pump-probe spectroscopy. The results I have obtained clarified interesting and previously ambiguous phenomena in these materials: SHG techniques supported a connection between ferroelectricity and superconductivity in SrTiO3, pump-probe spectroscopy explained the origin of CDW order in CsV3Sb5.