Multigap superconductivity at extremely high temperature: a model for the case of pressurized H2S

TL;DR

This paper models multigap superconductivity in pressurized H2S, showing how different electronic and phononic components contribute to high-temperature superconductivity within a BCS framework.

Contribution

It introduces a multiband BCS model for pressurized H2S, highlighting the role of two electronic components and phonon modes in achieving high-temperature superconductivity.

Findings

Two-gap superconductivity phenomenology in H2S.

High T_c achieved via interplay of soft and hard phonon modes.

Inter-band exchange enhances superconductivity.

Abstract

It is known that in pressurized H2S the complex electronic structure in the energy range of 200 meV near the chemical potential can be separated into two electronic components, the first characterized by steep bands with a high Fermi velocity and the second by flat bands with a vanishing Fermi velocity. Also the phonon modes interacting with electrons at the Fermi energy can be separated into two components: hard modes with high energy around 150 meV and soft modes with energies around 60 meV. Therefore we discuss here a multiband scenario in the standard BCS approximation where the effective BCS coupling coefficient is in the range 0.1- 0.32. We consider a first (second) BCS condensate in the strong (weak) coupling regime 0.32 (0.15). We discuss different scenario segregated in different portions of the material. The results show the phenomenology of unconventional superconducting phases in this two-gap superconductivity scenario where there are two electronic components in two Fermi surface spots, the pairing is mediated by either by a soft or a hard phonon branch where the inter-band exchange term, also if small, plays a key role for the emergence of high temperature superconductivity in pressurized sulfur hydride.