Superconducting hydrogen tubes in hafnium hydrides at high pressure
Kun Gao, Wenwen Cui, Ju Chen, Qinfang Wang, Jian Hao, Jingming Shi, Cailong Liu, Silvana Botti, Miguel A. L. Marques, Yinwei Li
Abstract
Compressing hydrogen-rich hydrides is an effective method to search for exotic properties such as high-${T}_{\text{c}}$ superconductivity. Here we show that high pressure and high temperature stabilize unique hydrogen tubes in hafnium hydrides. A combination of structural searches and first-principle calculations predict a metastable stochiometric ${\mathrm{HfH}}_{9}$ at 200 GPa. ${\mathrm{HfH}}_{9}$ is composed of H tubes intercalated within Hf-H framework, where two-thirds of the hydrogen atoms are arranged in a tubelike ${\mathrm{H}}_{12}$ structure located inside channels formed by the remainder ${\mathrm{HfH}}_{3}$. Each ${\mathrm{H}}_{12}$ tube gains 0.876 electrons from the ${\mathrm{HfH}}_{3}$ framework, indicating the ionic character of ${\mathrm{HfH}}_{9}$. Calculations show that ${\mathrm{HfH}}_{9}$ is a potential superconductor with an estimated ${T}_{\text{c}}$ of 110 K at 200 GPa, with the electron-phonon coupling arising mainly from the ${\mathrm{H}}_{12}$ tube and its interaction with the ${\mathrm{HfH}}_{3}$ framework. The current results suggest the existence of diverse hydrogen chemistries at high pressure that could be unravelled by future experimental studies.