| Using high-pressure Raman spectroscopy, this dissertation investigates several areas of condensed matter physics. With metal thiophosphates (MnPS{dollar}sb3{dollar}, NiPS{dollar}sb3){dollar} as our reference systems, we investigate coupling between phonons and two-magnon continua. We find that MnPS{dollar}sb3{dollar}'s two-magnon excitation can be tuned into resonance with the 155 cm{dollar}sp{lcub}-1{rcub}{dollar} phonon at a temperature near 60 K. In NiPS{dollar}sb3{dollar}, we find that the two-magnon excitation has a linewidth broader than that predicted by standard two-magnon theory, reminiscent of the similar linewidth observed in the undoped cuprate superconductors. This observation calls into question the role quantum fluctuations associated with spin 1/2 play in the cuprates' two-magnon spectrum. Additionally, high-pressure Raman measurements of NiPS{dollar}sb3{dollar} yielded evidence of resonant enhancement of the two-magnon excitation--previously only observed in the cuprate superconductors.; Additionally, we investigated the rutile-to-CaCl{dollar}sb2{dollar} ferroelastic phase transition occurring in RuO{dollar}sb2.{dollar} We observed the splitting of the (rutile) {dollar}Esb{lcub}g{rcub}{dollar} mode, and used this to find a transition pressure of 11.8 GPa. Based on the lower transition pressure found in previous work and on other results in the literature, we speculate that stoichiometry plays a critical role in determining the stability of the rutile or CaCl{dollar}sb2{dollar} phase of the metal dioxides.; These experiments were performed with a variety of single-, double-, and triple-grating spectrometers (Renishaw, SPEX, and Dilor, respectively). The excitation sources used were primarily ion lasers (either argon or helium-neon). Pressures up to 35 GPa were achieved via a Mao-Bell style Diamond Anvil Cell. |
