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VOLUME 89 (2009) | ISSUE 4 | PAGE 198
Evidence of maximum in the melting curve of hydrogen at megabar pressures
PACS: 62.50.-p, 64.70.dj, 67.63.Cd, 67.80.ff
Abstract
Hydrogen at high pressures of {\sim} 400 GPa might be in a zero-temperature liquid ground state (N. Ashcroft, J. Phys. Condens. Matter A 12, 129 (2000), E. G. Brovman et al., Sov. Phys. JETP 35, 783 (1972)). If metallic hydrogen is liquid, the melting T melt(P) line should possess a maximum. Here we report on the experimental evaluation of the melting curve of hydrogen in the megabar pressure range. The melting curve of hydrogen has been shown to reach a maximum with T_{\rm melt}= 1050\pm60 K at P =106 GPa and the melting temperature of hydrogen decreases at higher pressures so that T_{\rm melt}= 880 \pm 50 K at P =146 GPa. The data were acquired with the aid of a laser heating technique where diamond anvils were not deteriorated by the hot hydrogen. Our experimental observations are in agreement with the theoretical prediction of unusual behavior of the melted hydrogen [S. Bonev et al., Nature 431, 669 (2004)].