Superconductivity at 161 K in thorium hydride ThH10: Synthesis and properties

Abstract

Highlights• Superconductivity in fcc-ThH10 at 159-161 K at the pressure 174 Gigapascals • Very wide interval of stability of fcc-ThH10 from 85 to 185 GPa. • Upper critical magnetic field ThH10 ~45 Т. • Novel discovered superhydride hcp-ThH9 with TC of 146 K (170 GPa) and upper critical field ~38 Т • Newly discovered thorium hydrides: I4/mmm-ThH4 and Cmc21-ThH6 Abstract Here we report targeted high-pressure synthesis of two novel high-TC hydride superconductors, P63/mmc-ThH9 and 3 ̅ -ThH10, with the experimental critical temperatures (TC) of 146 K and 159-161 K and upper critical magnetic fields (μHC) 38 and 45 Tesla at pressures 170-175 Gigapascals, respectively. Superconductivity was evidenced by the observation of zero resistance and a decrease of TC under external magnetic field up to 16 Tesla. This is one of the highest critical temperatures that has been achieved experimentally in any compounds, along with such materials as LaH10, H3S and HgBa2CaxCu2O6+z. Our experiments show that fcc-ThH10 has stabilization pressure of 85 GPa, making this material unique among all known high-TC metal polyhydrides. Two recently predicted Th-H compounds, I4/mmm-ThH4 (> 86 GPa) and Cmc21-ThH6 (86-104 GPa), were also synthesized. Equations of state of obtained thorium polyhydrides were measured and found to perfectly agree with the theoretical calculations. New phases were examined theoretically and their electronic, phonon, and superconducting properties were calculated.Graphical Abstract

Classifying superconductivity in ThH-ThD superhydrides/superdeuterides

“…Semenok et al [44] also reported on the discovery of another high-temperature superconducting phase of ThH 10 at P=174 GPa, which exhibitsFm m 3 crystallographic symmetry and superconducting transition temperature of T c =159 K. In figure 3 we show raw upper critical field, B c2 (T), data for this phase [44] and data fit to equations (3)- (6).…”

“…Semenok et al [44] reported the discovery of a high-temperature superconducting phase of ThH 9 at P=170 GPa which exhibits P6 3 /mmc crystallographic symmetry and superconducting transition temperature of T c =146 K. They also performed first principles calculations and deduced the effective mass in this superconductor: As we mentioned in our previous papers [12,13,46,47], first principles calculations [39,48,49] always provide α-values near 5, which is the very strong-coupling limit for s-wave symmetry (also note that other superconducting gap symmetries have weak-coupling limits of α∼5 [50][51][52]). Despite the orthodox view, several new, alternative, approaches were developed to explain NRT superconductivity in compressed hydrides: Hirsch and Marsiglio [53], Souza and Marsiglio [54], Harshman and Fiory [55], as well as Kaplan and Imry [56].…”

“…Assuming all hydrogen-rich superconductors have the same primary mechanism for the superconductivity, the value of α=3.53 was taken as the lower bound for our calculations. 6)) for ThH 10 superhydride compressed at pressure P=174 GPa (raw data is from [44] Semenok et al [44] measured B c2 (T) for ThH 9 at P=170 GPa, which we fit to equations (3)-(6) in figure 2. This give T c /T F ratios that are within usual range of unconventional superconductors band, see figure 1.…”

“…Superconducting upper critical field, B c2 (T), data and fits to three different models (equations (3)-(6)) for ThH 9 superhydride compressed at pressure P=170 GPa (raw data is from[44]). (a) Fit to WHH and B-WHH models, for latter the fit quality is R=0.998.…”

Characterization of Near-Room-Temperature Superconductivity in Yttrium Superhydrides

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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.

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