Pressure-induced Superconductivity in the Hydrogen-dense material YH$_3$

The results presented by us allow for an understanding of pressure-induced superconductivity of tri-hydrides with a particular focus on YH$_3$. We show that a structural phase transition from hexagonal to cubic structure occurs at 20 GPa, which is in good agreement with recent experiments. This structural phase transition is seen to be accompanied by an insulator-to-metal transition in our quasi-particle calculations. Furthermore, we present an analysis of the superconducting behavior in cubic YH$_3$. At the lowest possible pressure (17.7 GPa), cubic YH$_3$ is superconducting with a T$_c$ of 40 K and turns into the normal metallic phase at 25 GPa due to a change of s-d hybridization between hydrogen and yttrium. This hitherto unprecedented low pressure should make superconducting YH$_3$ a very attractive system to study experimentally among the hydrogen-rich superconductors. Finally, we also predict that the superconducting phase reemerges at 45 GPa. J. S. de Almeida, D. Y. Kim, C. Ortiz, M. Klintenberg, and R. Ahuja, Appl. Phys. Lett.{\bf 94} 251913 (2009). D. Y. Kim, R. H. Scheicher, R. Ahuja, Phys. Rev. Lett. {\bf 103}, 077002 (2009).