Ionic structure, Liquid-liquid phase transitions, X-Ray diffraction, and X-Ray Thomson scattering in shock compressed liquid Silicon in the 100-200 GPa regime

Recent cutting-edge experiments have provided $in\,situ$ structure characterization and measurements of the pressure ($P$), density ($\bar{\rho}$) and temperature ($T$) of shock compressed silicon in the 100 GPa range of pressures and up to $\sim$10,000K. We present first-principles calculations in this $P,T,\bar{\rho}$ regime to reveal a plethora of novel liquid-liquid phase transitions (LPTs), making the interpretation of these experiments very challenging. The short-ranged ionic structure of the fluid is preserved under collective adjustments of many distant atoms when subject to compression and heating, with surprisingly little change in electrical and thermal conductivities $\sigma$ and $\kappa$. We match the experimental X-Ray Thompson scattering and X-ray diffraction data theoretically, and provide pressure isotherms, ionization data and compressibilities that support the above picture of liquid silicon as a highly complex LPT-driven ``glassy'' metallic liquid. These novel results are relevant to materials research, studies of planetary interiors, high-energy-density physics, and in laser-fusion studies.