Characterization of Near-Room-Temperature Superconductivity in Yttrium Superhydrides

Abstract

Recently, Troyan et al (2019 arXiv:1908 and Kong et al (2019 arXiv:1909 extended near-room-temperature superconductors family by new yttrium superhydride polymorphs, YHn (n = 4,6,7,9), which exhibit superconducting transition temperatures in the range of Tc = 210-243 K at pressure of P = 160-255 GPa. In this paper, temperature dependent upper critical field data, Bc2(T), for highly-compressed mixture of YH4+YH6 phases (reported by Kong et al 2019 arXiv:1909) is analysed to deduce the ratio of Tc to the Fermi temperature, TF. Our analysis shows that in all considered scenarios the YH4+YH6 mixture has the ratio 0.01 ≤ Tc/TF ≤ 0.04. As the result, YH4+YH6 falls in the unconventional superconductors band in the Uemura plot. It is also found that the characteristic temperature of the order parameter amplitude fluctuations, Tfluc, in the YH4+YH6 mixture is only several percent above observed Tc, and thus the superconducting transition in yttrium superhydride polymorphs is fundamentally limited by thermodynamics fluctuations.

Unconventional superconductivity in highly-compressed unannealed sulphur hydride

“…As the result, unannealed H3S (P = 155 GPa) phase in all considered scenarios (Table 1) has 0.02 ≤ Tc/TF ≤ 0.05 and falls in unconventional superconductors band of the Uemura plot [16][17][18] in close proximity to other NRT counterparts [1,2,[12][13][14][15] (Fig. 2), including annealed Most of NRT superconductors have severe influence of thermodynamic fluctuations on the superconducting order parameter and, thus, on the observed superconducting transition temperature, Tc [39][40][41]. There are two types of the thermodynamic fluctuations in superconductors, the phase fluctuations of the order parameter, which have characteristic temperature [42]: where  = (0)/(0) is Ginzburg-Landau parameter, and (0) is the ground state London penetration depth; and the amplitude fluctuations of the order parameter [43], with characteristic temperature of:…”

“…Raw data is taken from[18,37,[39][40][41]. Characteristic lines for the Bose-Einstein condensate (BEC) and the Bardeen-Cooper-Schrieffer (BCS) superconductors are shown for clarity.Most of NRT superconductors have severe influence of thermodynamic fluctuations on the superconducting order parameter and, thus, on the observed superconducting transition temperature, Tc[39][40][41]. There are two types of the thermodynamic fluctuations in superconductors, the phase fluctuations of the order parameter, which have characteristic temperature[42]:…”