Few systems have Tc values above 30 K since mercury’s superconductivity was found over a century ago.
ShanghaiTech University and Renmin University of China have observed superconductivity up to 32 K in MoB2 under pressure—the greatest Tc in transition-metal borides to date.
Their February 14, 2023 National Science Review article discusses high-Tc superconductors in transition metal borides.
Molybdenum diboride (MoB2) is unique in the MB2 family since it possesses both an AlB2-type and a CaSi2-type phase. Synchrotron X-Ray diffraction (XRD) shows that above 65 GPa, β-MoB2 transforms to α-MoB2, which has the same crystal structure as MgB2.
A question arises naturally: is it possible to achieve superconductivity in MoB2 under high pressure. So, we carried out the in-situ high pressure electrical transport measurements. Superconductivity is observed at 21.7 GPa and Tc increases with pressure.
Unlike MgB2, where the p-electrons and phonon modes of B atoms dominate superconductivity, the compressed MoB2’s superconducting mechanism is dominated by the transition metal Mo atoms’ d-electrons and phonon modes.
This work highlights transitional metals’ overlooked roles in borides’ superconductivity.
Their discovery of MoB2’s superconductivity at a high Tc could illuminate the exploration of high-Tc superconductivity in systems with light elements due to the synergistic effects of light elements with high-frequency phonon modes and strongly correlated electrons in transition metals.
The Beijing Natural Science Foundation, the National Natural Science Foundation of China, the CAS Interdisciplinary Innovation Team, the National Key R&D Program, the Fundamental Research Funds for Central Universities, and the Renmin University of China Research Funds generously supported this work.