What makes the Tc of monolayer FeSe on SrTiO3 so high: a sign-problem-free quantum Monte Carlo study

TL;DR

This study uses sign-problem-free quantum Monte Carlo simulations to investigate the high superconducting transition temperature of monolayer FeSe on SrTiO3, focusing on intrinsic pairing mechanisms, electron-phonon interactions, and nematic fluctuations.

Contribution

It provides the first numerically-exact simulations to analyze the effects of electron-phonon interactions and nematic fluctuations on Tc in iron-based superconductors.

Findings

Intrinsic pairing mechanisms contribute significantly to Tc.

Electron-phonon interactions enhance superconductivity.

Nematic fluctuations influence the pairing dynamics.

Abstract

Monolayer FeSe films grown on SrTiO3 (STO) substrate show superconducting gap-opening temperatures (Tc) which are almost an order of magnitude higher than those of the bulk FeSe and are highest among all known Fe-based superconductors. Angle-resolved photoemission spectroscopy (ARPES) observed "replica bands" suggesting the importance of the interaction between FeSe electrons and STO phonons. These facts rejuvenated the quest for Tc enhancement mechanisms in iron-based, especially iron-chalcogenide, superconductors. Here, we perform the first numerically-exact sign-problem-free quantum Monte Carlo simulations to iron-based superconductors. We (i) study the electronic pairing mechanism intrinsic to heavily electron doped FeSe films, and (ii) examine the effects of electron-phonon interaction between FeSe and STO as well as nematic fluctuations on Tc. Armed with these results, we return to the question "what makes the Tc of monolayer FeSe on SrTiO3 so high?" in the conclusion and discussions.