Analysis of heating curves and optical properies for the liquid-liquid transition to metallic hydrogen

Hydrogen at high temperatures and pressures undergoes a phase transition from liquid molecular to liquid atomic metallic hydrogen. This transition takes place on the planet Jupiter and has been studied in the laboratory. Experiments in a diamond anvil cell for temperatures up to 2000 K and pressures of 100-170 GPa determine heating curves and optical properties. Heating curves (the temperature of the sample as a function of heating power) have a positive slope with increasing power with a plateau in temperature, most likely associated with the latent heat of transformation. Plateaus are associated with an abrupt rise in reflectance and absorption of visible light as expected for a metal. We carry out a realistic finite element analysis of heating curves and optical properties. The simulation shows that the plateaus and onset of absorption are related to the phase transition. However much larger values of latent heat are required than have been predicted by theory. The transition may be more complex than considered in current models.