aCondensed Matter Theory Group, Department of Physics and Materials Science, Uppsala University, Box 530 SE-751 21, Uppsala, Sweden;
bTheory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom;
cGeophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015;
dQuantum Functional Semiconductor Research Center and Department of Physics, Dongguk University, Seoul 100-715, Korea; and
eApplied Material Physics, Department of Materials Science and Engineering, Royal Institute of Technology (KTH) SE-100 44, Stockholm, Sweden
Contributed by Ho-Kwang Mao, December 15, 2009 (sent for review November 28, 2009)
The long-standing prediction that hydrogen can assume a metallic state under high pressure, combined with arguments put forward more recently that this state might even be superconducting up to high temperatures, continues to spur tremendous research activities toward the experimental realization of metallic hydrogen. These efforts have however so far been impeded by the enormous challenges associated with the exceedingly large required pressure. Hydrogen-dense materials, of the MH4 form (where M can be, e.g., Si, Ge, or Sn) or of the MH3 form (with M being, e.g., Al, Sc, Y, or La), allow for the rather exciting opportunity to carry out a proxy study of metallic hydrogen and associated high-temperature superconductivity at pressures within the reach of current techniques. At least one experimental report indicates that a superconducting state might have been observed already in SiH4, and several theoretical studies have predicted superconductivity in pressurized hydrogen-rich materials; however, no systematic dependence on the applied pressure has yet been identified so far. In the present work, we have used first-principles methods in an attempt to predict the superconducting critical temperature (Tc) as a function of pressure (P) for three metal-hydride systems of the MH3 form, namely ScH3, YH3, and LaH3. By comparing the obtained results, we are able to point out a general trend in the Tc-dependence on P. These gained insights presented here are likely to stimulate further theoretical studies of metallic phases of hydrogen-dense materials and should lead to new experimental investigations of their superconducting properties.