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.

Terapascal iron-melting temperature: The pressure and temperature conditions at which iron melts are important for terrestrial planets because they determine the size of the liquid metal core, an important factor for understanding the potential for generating a radiation-shielding magnetic field. Kraus et al . used laser-driven shock to determine the iron-melt curve up to a pressure of 1000 gigapascals (see the Perspective by Zhang and Lin). This value is about three times that of the Earth’s inner core boundary. The authors found that the liquid metal core lasted the longest for Earth-like planets four to six times larger in mass than the Earth. —BG

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 ${\mathrm{LaH}}_{10}$.

Recent computational studies have predicted that rare-earth superhydrides are promising high-temperature superconductors. Of these phases having very high hydrogen content ($\mathrm{X}{\mathrm{H}}_n,n>6$, where X is the rare-earth atom) a cubic phase of lanthanum hydride, recently synthesized at 170 GPa and identified as $\mathrm{La}{{\mathrm{H}}_{10}}_{\pm x}$, is in good agreement with theoretical predictions. The experiments found that the stability of the phase extended to lower pressure and a distorted form was found on decompression. Here we examine the nuclear quantum effects and anharmonic dynamics on $\mathrm{La}{\mathrm{H}}_{10}$, including the behavior of the hydrogen sublattice in comparison with the predicted atomic metallic hydrogen at higher pressure. We also examine the vibrational dynamics and electronic properties of a distorted lower pressure phase of $\mathrm{La}{\mathrm{H}}_{10}$ and find that superconducting $T_c$ decreases relative to cubic but remains relatively high (i.e., 229–245 K).

The recent theory-driven discovery of a class of clathrate hydrides (e.g., CaH ₆ , YH ₆ , YH ₉ , and LaH ₁₀ ) with superconducting critical temperatures ( T _c ) well above 200 K has opened the prospects for “hot” superconductivity above room temperature under pressure. Recent efforts focus on the search for superconductors among ternary hydrides that accommodate more diverse material types and configurations compared to binary hydrides. Through extensive computational searches, we report the prediction of a unique class of thermodynamically stable clathrate hydrides structures consisting of two previously unreported H ₂₄ and H ₃₀ hydrogen clathrate cages at megabar pressures. Among these phases, LaSc ₂ H ₂₄ shows potential hot superconductivity at the thermodynamically stable pressure range of 167 to 300 GPa, with calculated T _c s up to 331 K at 250 GPa and 316 K at 167 GPa when the important effects of anharmonicity are included. The very high critical temperatures are attributed to an unusually large hydrogen-derived density of states at the Fermi level arising from the newly reported peculiar H ₃₀ as well as H ₂₄ cages in the structure. Our predicted introduction of Sc in the La–H system is expected to facilitate future design and realization of hot superconductors in ternary clathrate superhydrides.