High-Temperature Superconducting Phase in Clathrate Calcium Hydride CaH6 up to 215 K at a Pressure of 172 GPa

The recent discovery of superconductive rare earth and actinide superhydrides has ushered in a new era of superconductivity research at high pressures. This distinct type of clathrate metal hydrides was first proposed for alkaline-earth-metal hydride CaH6 that, however, has long eluded experimental synthesis, impeding an understanding of pertinent physics. Here, we report successful synthesis of CaH6 and its measured superconducting critical temperature T-c of 215 K at 172 GPa, which is evidenced by a sharp drop of resistivity to zero and a characteristic decrease of T-c under a magnetic field up to 9 T. An estimate based on the Werthamer-Helfand-Hohenberg model gives a giant zero-temperature upper critical magnetic field of 203 T. These remarkable benchmark superconducting properties place CaH6 among the most outstanding high-T-c superhydrides, marking it as the hitherto only clathrate metal hydride outside the family of rare earth and actinide hydrides. This exceptional case raises great prospects of expanding the extraordinary class of high-T-c superhydrides to a broader variety of compounds that possess more diverse material features and physics characteristics.

Automated summary

The discovery of superconductive rare earth and actinide superhydrides has opened up a new era of high-pressure superconductivity research. The successful synthesis of CaH6 and its remarkable superconducting properties highlight the potential for further exploration and development of high-temperature superconducting materials.