Superconducting I43m CSH7 Model Applied to Resistive Transition Temperature Data for Compressed C-S-H at High Pressure

By | | High-Tc superconductivity, High-Tc theory, Transition temperature

Superconducting I43m CSH7 Model Applied to Resistive Transition Temperature Data for Compressed C-S-H at High Pressure, Dale R. Harshman and Anthony T. Fiory [arXiv_2]

This article updates version 1 by restricting consideration to only the resistive data and excluding the questioned 287.7-K datum reported for carbonaceous sulfur hydride in Snider et al., Nature 585, 373 (2020). The superconducting transitions are considered in terms of the theoretically-discovered compressed I43m CSH7 structure of Sun et al., Phys. Rev. B 101, 174102 (2020), which comprises a sublattice similar to Im3m H3S with CH4 intercalates. Positing an electronic genesis of the superconductivity, a model is presented in analogy with earlier work on superconductivity in Im3m H3S, in which pairing is induced via purely electronic Coulomb interactions across the mean distance ζ between the S and H4 tetrahedra enclosing C. Theoretical superconducting transition temperatures for I43m CSH7 are derived as TC0 = (2/3)1/2σ1/2β/aζ, where β = 1247.4 Å2K is a universal constant, σ is the participating charge fraction, and a is the lattice parameter. Analysis suggests persistent bulk superconductivity with a pressure-dependent σ, increasing from σ = 3.5, determined previously for Im3m H3S, to σ = 7.5 at high pressure owing to additionally participating C-H bond electrons. With an and ζ determined by theoretical structure, calculations of TC0 at the highest pressures, 258 and 271 GPa, are in agreement with resistive transitions to within an overall uncertainty of ± 3.5 K.

FIG. 1. Schematic structure of I43m CSH7, indicating the four distances ζ1, ζ2, ζ3, and ζ4 for calculating the average ζ, the H4-tetrahedron, and coordinates of S ions located at cube corners.
FIG. 2. The extracted σ(X) from resistance data (open circles) as defined in Eq. (3), plotted as a function of pressure P. The solid blue curve is a fit of the function σ(em>P) from Eq. (5) to the data. The dotted curves represent the calculated uncertainty. The dashed horizontal lines at 3.5, 5.5, and 7.5 correspond to charge fractions for H3S (7/2), H3S + H4 (11/2), and H3S + CH4 (15/2), respectively. Questioned resistive datum: pink color.
FIG. 3. Measured resistance transition temperature TC vs. pressure P after Ref. 1 (open circles). The solid blue curve is TC0(P) from Eq. (6) to the data. The dotted blue curves represent the calculated uncertainty. Questioned resistive datum: pink color.
FIG. 4. Measured TC vs. calculated TC0 for compressed high-TC superconductors; I43m CSH7 (258-271 GPa), Fm3m LaH10 (169 and 192 GPa) [29], Im3m H3S (155 GPa) [27], HgBa2Ca2Cu3O8+δ (25 GPa) [28], YBa2Cu3O8 (12 GPa) [29], A15 Cs3C60 (0.93 GPa) [30], FeSe0.977 (7.5 GPa) [43], Fe1.03Se0.57Te0.43 (2.3 GPa) [43], and C/C (twisted bilayer graphene device D2, 1.33 GPa) [44]. The solid line represents Eq. (1), highlighting the equality between TC and TC0.

Dale R. Harshman and Anthony T. Fiory, arXiv:2201.01860v2 [cond-mat.supr-con] (2023).

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