Superconductivity in RbH$_{12}$ at low pressures: An ab initio study

High-pressure polyhydrides are leading contenders for room temperature superconductivity. The next frontier lies in stabilizing them at ambient pressure, which would allow their practical applications. In this first-principles computational study, we investigate the potential for record-low pressure stabilization of binary superhydrides within the RbH _{12} <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msub> <mml:mi/> <mml:mn>12</mml:mn> </mml:msub> </mml:math> system including lattice quantum anharmonic effects in the calculations. We identify five competing phases for the pressure range between 0 and 100 GPa. Incorporating anharmonic and quantum effects on ion dynamics, we find the Immm <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mi>I</mml:mi> <mml:mi>m</mml:mi> <mml:mi>m</mml:mi> <mml:mi>m</mml:mi> </mml:mrow> </mml:math> and P6_3/mmc <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mi>P</mml:mi> <mml:msub> <mml:mn>6</mml:mn> <mml:mn>3</mml:mn> </mml:msub> <mml:mi>/</mml:mi> <mml:mi>m</mml:mi> <mml:mi>m</mml:mi> <mml:mi>c</mml:mi> </mml:mrow> </mml:math> phases to be the most probable, potentially metastable even at pressures as low as 10 GPa. Notably, all phases exhibit metallic properties, with critical temperatures between 46 and 111 K within the pressure range they are dynamically stable. These findings have the potential to inspire future experimental exploration of high-temperature superconductivity at low pressures in Rb-H binary compounds.