Transition to Metallic Phase of Fluid Hydrogen at High Pressure and High Temperature*

We investigated the phase transition to the metallic fluid phase of hydrogen under high pressure and high temperature by the laser heated diamond-anvil cell (LHDAC) up to 100 GPa and 2500 K. Compressed hydrogen was heated by IR laser with a thin gold foil, acts as the laser absorber. The temperature of hydrogen was determined from the thermal radiation spectrum from the gold foil at each laser power. The measured temperature vs. laser power curves showed the maxima at pressures above 80 GPa. These results indicate that the absorptance changed around the gold foil, which may due to a phase transition in hydrogen at the pressure and temperature. We confirmed that no anomaly in the curves was observed without hydrogen.