Development of an ultrafast pump-probe spectroscopy system and its application to pressure-tuned organic superconductors

In this study, we developed an optical pump-probe spectroscopy measurement system that operates at high pressures and low temperatures by combining a diamond anvil cell with a commercially available cryostat. The current setup allows for optical measurements at pressures up to 10 GPa and temperatures as low as approximately 13 K. As a demonstration, we examined the effects of pressure on the photo-induced pseudogap formation at a temperature Tg of approximately 70 K in the organic superconductor κ-(BEDT-TTF)2Cu(NCS)2. At a pressure of 0.8 GPa, we observed changes in transient reflectivity associated with pseudogap formation occurring below approximately 200 K, which is above Tg. This finding suggests that pressure influences the electron-phonon interaction, leading to the development of a pseudogap at higher temperatures.