Compressed H 3 S: inter-sublattice Coulomb coupling in a high-T C superconductor

• Published in: Journal of physics. Condensed matter Vol. 29; no. 44; p. 445702
• Main Authors: Harshman, Dale R, Fiory, Anthony T
• Format: Journal Article
• Language: English
• Published: England 08.11.2017
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/1361-648X/aa80d0

Upon thermal annealing at or above room temperature (RT) and at high hydrostatic pressure P ~ 155 GPa, sulfur trihydride H S exhibits a measured maximum superconducting transition temperature T ~ 200 K. Various theoretical frameworks incorporating strong electron-phonon coupling and Coulomb repulsion have reproduced this record-level T . Of particular relevance is that experimentally observed H-D isotopic correlations among T , P, and annealed order indicate an H-D isotope effect exponent α limited to values  ⩽  0.183, leaving open for consideration unconventional high-T superconductivity with electronic-based enhancements. The work presented herein examines Coulombic pairing arising from interactions between neighboring S and H species on separate interlaced sublattices constituting H S in the Im[Formula: see text]m structure. The optimal value of the transition temperature is calculated from T   =  [Formula: see text]Λe /[Formula: see text] ζ, with Λ  =  0.007465 Å, inter-sublattice S-H separation spacing ζ  =  a /[Formula: see text], interaction charge linear spacing [Formula: see text] =  a (3/σ) , average participating charge fraction σ  =  3.43  ±  0.10 estimated from calculated H-projected electron states, and lattice parameter a   =  3.0823 Å at P  =  155 GPa. The resulting value of T   =  198.5  ±  3.0 K is in excellent agreement with transition temperatures determined from resistivity (196-200 K onsets, 190-197 K midpoints), susceptibility (200 K onset), and critical magnetic fields (203.5 K by extrapolation). Analysis of mid-infrared reflectivity data confirms the expected correlation between boson energy and ζ . Suppression of T below T , correlating with increasing residual resistance for  <  RT annealing, is treated in terms of scattering-induced pair breaking. Correspondences between H S and layered high-T superconductor structures are also discussed, and a model considering Compton scattering of virtual photons of energies  ⩽  e /ζ by inter-sublattice electrons is introduced, illustrating that Λ  ∝  ƛ , where ƛ is the reduced electron Compton wavelength.