A Schematic Two Overlapping-Band Model for Superconducting Sulfur Hydrides: The Isotope Mass Exponent

Abstract

The high value of the isotope shift in sulfur hydrides supports a phonon-mediated pairing scenario of superconductivity for these high-temperature superconductors which are consistent with the Bardeen–Cooper–Schrieffer (BCS) framework. Knowing that a large electronic density of states enhances the critical temperature (Tc), generalized Fermi surface topologies are used to increase it. A multicomponent model within the BCS framework is proposed in this work for sulfur hydride superconductors. This model is used to evaluate some properties of the H3S superconductor. Strong and intermediate coupling effects are taken into account with the effective McMillan approximation, and the isotope coefficient is evaluated as a function of the coupling parameter as well as other relevant parameters of the model.

Isotope effect in superconducting lanthanum hydride under high compression

“…5). The present theory and previous experimental data showing that T c varies with the isotopic mass provide a strong evidence for the interaction between the electrons and lattice vibrations [43][44][45]. We further analyze the isotope effect of T c in terms of the isotope coefficient (α), which is given by the following relation:…”

Multi-Band Superconductivity and the Steep Band/Flat Band Scenario

“…These results show that cuprates, diborides [72][73][74] and iron based superconductors [75] are close to Lifshitz transitions for the appearance of a Fermi surface spot. The special case of the steep band/flat band scenario in the multiband superconductors admits for further increases in TC and it has been proposed to be applicable to hydrogen based superconductors [76][77][78][79] where pressure tunes the system at electronic topological transitions [80,81], with the formation of a complex scenario made of a nanoscale phase separation where free particles and polarons coexist in a scale invariant texture [82].…”