Energy gap in hydride superconductors due to spin-amplified phonons

Abstract

Room temperature superconductivity has been realized in hydrides under ultrahigh pressure. A recent study has revealed that charge pairing in pressurized hydrides is mediated by spin-amplified phonons. Little research has been undertaken to reveal the energies involved in pressurized superconductivity. In this paper, we study the evolution of the energy gap under immense pressure in hydride superconductors. We adopt the non-standard BCS theory in which multiple bands with different symmetry cross the chemical potential and multiple gaps form in different spots of the k-space and all multiple Fermi surfaces are in the BCS limit. The energy Epen>ℏωD due to enhanced phonons produces multiple bandgaps. Applying the multiband BCS model in the presence of spin-amplified phonons reveals electron–phonon coupling beyond the Eliashberg–Migdal limit. The energy gap function Δ0 in the strong electron–phonon coupling limit shows dependence on ionic spin and Tc in which the effect of pressure and phonons on the gap is confined. Further, we show that pressure at Tc→0 is nonzero.