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Abstract:
Since the discovery of superconductivity at 200 K in H3S [1], similar or higher
transition temperatures, Tcs, 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 Tc, the shift of Tc to lower
temperatures under external magnetic fields, and pronounced isotope effect.
Remarkably, the results are in good agreement with the theoretical predictions, which
describe superconductivity in hydrides within the framework of the conventional BCS
theory.
Magnetic properties, one of the most important characteristics of a superconductor,
have not been satisfactorily defined. Recently, we develop SQUID magnetometry
under extremely high-pressure conditions [3, 4] 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 λL 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 [4]. This technique provides a strong
magnetic response and, what is more important, eliminates the huge background of a
bulky diamond anvil cell. We will present also new methods and results.
A large part of the report will be a discussion of progress in increasing Tc to room
temperature and above at high pressures and substantial superconductivity at low
pressures.
References
1. Drozdov, A.P., et al., Conventional superconductivity at 203 K at high pressures.
Nature 2015. 525: p. 73.
2. Flores-Livas, J.A., et al., A perspective on conventional high-temperature
superconductors at high pressure: Methods and materials. Phys. Rep., 2020. 856:
p. 1-78.
3. Minkov, V.S., et al., Magnetic field screening in hydrogen-rich high-temperature
superconductors. Nature Communications, 2022.
4. Minkov, V.S., et al., Trapped magnetic flux in hydrogen-rich high-temperature
superconductors arXiv:2206.14108 2022.
