This paper discusses where and how high-temperature superconductors can be found.

Recent reports of the superconductivity in hydrides of two different families (covalent lattice, as in SH₃ and clathrate-type H-cages containing La and Y atoms, as in LaH₁₀ and YH₆) have revealed new families of high-T_c materials with T_c’s near room temperature values. These findings confirm earlier expectations that hydrides may have very high T_c’s due to the fact that light H atoms have very high vibrational frequencies, leading to high T_c values within the conventional Bardeen–Cooper–Schrieffer phonon mechanism of superconductivity. However, as is pointed out by Ashcroft, it is important to have the metallic hydrogen “alloyed” with the elements added to it. This concept of a metallic alloy containing a high concentration of metal-like hydrogen atoms has been instrumental in finding new high-T_c superhydrides. These new superhydride “room-temperature” superconductors are stabilized only at very high pressures above 100 GPa, making the experimental search for their superconducting properties very difficult. We will review the current experimental and theoretical results for LaH_10?x and YH_6?x superhydrides.