Superconductivity in Superhydrides—New Experimental Developments

Since the discovery of superconductivity at ~ 200 K in H₃S [1], similar or higher transition temperatures, <i>T_c</i>s, have been reported for various hydrogen-rich compounds under ultra-high pressures [2]. Superconductivity was experimentally proved by different methods, including electrical resistance, magnetic susceptibility, optical infrared, and nuclear resonant scattering measurements. The crystal structures of superconducting phases were determined by X-ray diffraction. Numerous electrical transport measurements demonstrate the typical behavior of a conventional phonon-mediated superconductor: zero resistance below <i>T_c</i>, the shift of <i>T_c </i>to lower temperatures under external magnetic fields, and pronounced isotope effect. Remarkably, the results agree with the theoretical predictions, which describe superconductivity in hydrides within the framework of the conventional BCS theory.<br/>Magnetic properties, one of the most important characteristics of a superconductor, have not been satisfactory defined. Recently, we developed SQUID magnetometry under extreme high-pressure conditions [3] and report characteristic superconducting parameters for H₃S and LaH₁₀—the representative members of two families of high-temperature superconducting hydrides. In particular, we determine a London penetration depth λ_L of ∼20 nm in H₃S and ∼30 nm in LaH₁₀. These compounds have the values of the Ginzburg-Landau parameter κ ∼12–20 and belong to the group of “moderate” type II superconductors. We further develop magnetic measurements with the trapped magnetic flux. This technique provides a strong magnetic response and, what is more important, eliminates the huge background of a bulky diamond anvil cell.<br/>A large part of the report will be a discussion of possibilities of further increasing <i>T_c</i> to room temperature and above, with emphasis on experimental espects.<br/><br/><br/><br/>1. Drozdov, A.P., et al., <i>Conventional superconductivity at 203 K at high pressures.</i> Nature 2015. <b>525</b>: p. 73.<br/>2. Flores-Livas, J.A., et al., <i>A perspective on conventional high-temperature superconductors at high pressure: Methods and materials.</i> Phys. Rep., 2020. <b>856</b>: p. 1-78.<br/>3. Minkov, V.S., et al., <i>Magnetic field screening in hydrogen-rich high-temperature superconductors.</i> Nature Communications, 2022.