Superconductivity in pressurized Re${}_{0.10}$Mo${}_{0.90}$B${}_2$

The recent surprising discovery of superconductivity with critical temperature $T_c$ = 32 K in MoB${}_2$ above 70 GPa has led to the search for related materials that may superconduct at similarly high $T_c$ values and lower pressures. We have studied the superconducting and structural properties of Re${}_{0.10}$Mo${}_{0.90}$B${}_2$ to 170 GPa. A structural phase transition from R3m to P6/mmm commences at 48 GPa, with the first signatures of superconductivity appearing above 44 GPa. The critical temperature is observed to increase with pressure. A complete resistive transition is observed only above 150 GPa, where the highest onset $T_c$ of 30 K is also achieved. Upon releasing pressure, the high pressure superconducting phase is found to be metastable. During unloading, a complete resistive superconducting transition is observed all the way down to 20 GPa (with onset $T_c\sim 20$ K). Our results suggest that the P6/mmm structure is responsible for the observed superconductivity.