title: Optical Properties of Fluid Hydrogen at the Transition to a Conducting State.
abstract: We use fast transient transmission and emission spectroscopies in the pulse laser heated diamond anvil cell to probe the energy-dependent optical properties of hydrogen at pressures of 10-150 GPa and temperatures up to 6000 K. Hydrogen is absorptive at visible to near-infrared wavelengths above a threshold temperature that decreases from 3000 K at 18 GPa to 1700 K at 110 GPa. Transmission spectra at 2400 K and 141 GPa indicate that the absorptive hydrogen is semiconducting or semimetallic in character, definitively ruling out a first-order insulator-metal transition in the studied pressure range.
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington D.C. 20015, USA.|School of Physics and Astronomy and Centre for Science at Extreme Conditions, University of Edinburgh, Peter Guthrie Tait Road, Edinburgh, United Kingdom EH9 3FD.|Department of Mathematics, Howard University, 2400 Sixth Street NW, Washington D.C. 20059, USA.
authors.forename: R Stewart
authors.initials: RS
authors.lastname: McWilliams
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington D.C. 20015, USA.
authors.forename: D Allen
authors.initials: DA
authors.lastname: Dalton
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington D.C. 20015, USA.|Department of Mathematics, Howard University, 2400 Sixth Street NW, Washington D.C. 20059, USA.
authors.forename: Mohammad F
authors.initials: MF
authors.lastname: Mahmood
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington D.C. 20015, USA.|Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, 350 Shushanghu Road, Hefei, Anhui 230031, China.|University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Alexander F
authors.initials: AF
authors.lastname: Goncharov