High $T_c$ superconductivity at the FeSe/SrTiO$_3$ Interface

TL;DR

This paper investigates how ferroelectric phonons at the FeSe/SrTiO3 interface enhance superconductivity, potentially increasing the pairing energy scale and altering pairing symmetry, which could influence understanding of high-temperature superconductivity.

Contribution

It demonstrates that interface phonons can significantly boost Cooper pairing and modify pairing symmetry in FeSe films, highlighting the importance of phonons in iron-based superconductors.

Findings

Superconducting gap in monolayer FeSe is much larger than in bulk.

Screening by ferroelectric phonons enhances Cooper pairing.

Phonons may alter pairing symmetry at the interface.

Abstract

In a recent experiment the superconducting gap of a single unit cell thick FeSe film on SrTiO$_3$ substrate is observed by scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy. The value of the superconducting gap is much larger than that of the bulk FeSe under ambient pressure. In this paper we study the effects of screening due to the ferroelectric phonons on Cooper pairing. We conclude it can significantly enhance the energy scale of Cooper pairing and even change the pairing symmetry. Our results also raise some concerns on whether phonons can be completely ignored for bulk iron-based superconductors.