Designing materials with advanced functionalities is the main focus of contemporary solid-state physics and chemistry. Research efforts worldwide are funneled into a few high-end goals, one of the oldest, and most fascinating of which is the search for an ambient temperature superconductor (A-SC). The reason is clear: superconductivity at ambient conditions implies being able to handle, measure and access a single, coherent, macroscopic quantum mechanical state without the limitations associated with cryogenics and pressurization. This would not only open exciting avenues for fundamental research, but also pave the road for a wide range of technological applications, affecting strategic areas such as energy conservation and climate change. In this roadmap we have collected contributions from many of the main actors working on superconductivity, and asked them to share their personal viewpoint on the field. The hope is that this article will serve not only as an instantaneous picture of the status of research, but also as a true roadmap defining the main long-term theoretical and experimental challenges that lie ahead. Interestingly, although the current research in superconductor design is dominated by conventional (phonon-mediated) superconductors, there seems to be a widespread consensus that achieving A-SC may require different pairing mechanisms. In memoriam, to Neil Ashcroft, who inspired us all.

The theoretical exploration of the phase diagrams of binary hydrides under pressure using ab initio crystal structure prediction techniques coupled with first principles calculations has led to the in silico discovery of numerous novel superconducting materials. This Perspective focuses on the alkaline earth and rare earth polyhydrides whose superconducting critical temperature, Tc, was predicted to be above the boiling point of liquid nitrogen. After providing a brief overview of the computational protocol used to predict the structures of stable and metastable hydrides under pressure, we outline the equations that can be employed to estimate Tc. The systems with a high Tc can be classified according to the motifs found in their hydrogenic lattices. The highest Tcs are found for cages that are reminiscent of clathrates and the lowest for systems that contain atomic and molecular hydrogen. A wide variety of hydrogenic motifs including 1- and 2-dimensional lattices, as well as H10δ− molecular units comprising fused H5δ− pentagons, are present in phases with intermediate Tcs. Some of these phases are predicted to be superconducting at room temperature. Some may have recently been synthesized in diamond anvil cells.

While exploring potential superconductors in the C-S-H ternary system using first-principles crystal structure prediction methods, we uncovered a class of hydride perovskites based on the intercalation of methane into an ${\mathrm{H}}_3\mathrm{S}$ framework. These intriguing ${\mathrm{H}}_3\mathrm{S}\text{−}{\mathrm{CH}}_4$ structures emerge as metastable at $\sim 100$ GPa. Electron-phonon coupling calculations indicate that phases with ${\mathrm{CSH}}_7$ stoichiometry are potential superconductors with $T_c$ values ranging from 100 K to 190 K at megabar pressures. The results are expected to guide the experimental search for new high-$T_c$ superconductors, including those stable at lower pressures than previously documented superconducting hydrides such as ${\mathrm{H}}_3\mathrm{S}$ and ${\mathrm{LaH}}_{10}$.

The stability, electronic structure, and potential superconductivity in AB₃Si₃ (A = Na, K, Rb, and Cs) compounds that assume a clathrate-based sodalite structure whose framework consists of covalent B–Si bonds are investigated via first-principles calculations. This structure type has recently been predicted in a number of high-temperature superconducting hydrides, but these are only stable under megabar pressures. Herein, we predict a novel superconducting phase, RbB₃Si₃, that could be synthesized under pressures that are smaller by a factor of 10, ∼10 GPa, and quenched to atmospheric conditions. Electron–phonon coupling calculations predict that RbB₃Si₃ possesses a superconducting critical temperature, T_c, of 14 K at 1 atm. The dynamic stability of RbB₃Si₃ and CsB₃Si₃ at ambient pressure can be explained by considering the chemical pressure exerted on the B–Si framework that is caused by the size effect of the alkali metal atom.