High-Temperature Superconductivity in Cerium Superhydrides

TL;DR

This paper reports the experimental discovery of superconductivity in cerium superhydrides at relatively low pressures, with critical temperatures up to 115 K, advancing the understanding of high-temperature superconductors in hydrides.

Contribution

First experimental demonstration of superconductivity in cerium superhydrides at pressures below 100 GPa, revealing new phases with high critical temperatures.

Findings

Superconductivity observed at 115 K in CeH10 at 95 GPa.

Two new phases, CeH10 and CeH9, exhibit superconductivity.

Maximum Tc of ~100 K in CeH9 at 130 GPa.

Abstract

The discoveries of high-temperature superconductivity in H3S and LaH10 have excited the search for superconductivity in compressed hydrides. In contrast to rapidly expanding theoretical studies, high-pressure experiments on hydride superconductors are expensive and technically challenging. Here we experimentally discover superconductivity in two new phases,Fm-3m-CeH10 (SC-I phase) and P63/mmc-CeH9 (SC-II phase) at pressures that are much lower (<100 GPa) than those needed to stabilize other polyhydride superconductors. Superconductivity was evidenced by a sharp drop of the electrical resistance to zero, and by the decrease of the critical temperature in deuterated samples and in an external magnetic field. SC-I has Tc=115 K at 95 GPa, showing expected decrease on further compression due to decrease of the electron-phonon coupling (EPC) coefficient {\lambda} (from 2.0 at 100 GPa to 0.8 at 200 GPa). SC-II has Tc = 57 K at 88 GPa, rapidly increasing to a maximum Tc ~100 K at 130 GPa, and then decreasing on further compression. This maximum of Tc is due to a maximum of {\lambda} at the phase transition from P63/mmc-CeH9 into a symmetry-broken modification C2/c-CeH9. The pressure-temperature conditions of synthesis affect the actual hydrogen content, and the actual value of Tc. Anomalously low pressures of stability of cerium superhydrides make them appealing for studies of superhydrides and for designing new superhydrides with even lower pressures of stability.