Superconducting gap and pseudogap in the surface states of the iron-based superconductor PrFeAsO$_{1-y}$ studied by angle-resolved photoemission spectroscopy

TL;DR

This study uses ARPES to reveal superconducting gaps and pseudogaps on surface states of PrFeAsO$_{1-y}$, indicating surface superconductivity possibly induced by the bulk and highlighting pseudogap characteristics of hole-doped iron superconductors.

Contribution

First ARPES investigation showing superconducting and pseudogap features on surface states of PrFeAsO$_{1-y}$, revealing surface-bulk interactions and pseudogap properties in hole-doped iron-based superconductors.

Findings

Superconducting gap observed on surface and bulk hole pockets.

Large pseudogap detected on surface-derived hole pockets.

Surface superconductivity may be induced by proximity effect.

Abstract

In order to study the possible superconductivity at the polar surfaces of 1111-type iron-based superconductors, which is doped with a large amount of holes in spite of the electron doping in bulk materials, we have performed angle-resolved photoemission spectroscopy (ARPES) studies on superconducting PrFeAsO$_{1-y}$~crystals. We have indeed observed the opening of a superconducting gap on surface-derived hole pockets as well as on a bulk-derived hole pocket. The superconducting gap is found to open on the surface-derived hole pockets below the bulk $T_c$, which suggests that the surface superconductivity is possibly induced by proximity effect from the bulk. We have also observed the opening of a large pseudogap on the surface-derived hole pockets, which is similar to the pseudogap in 122-type bulk superconductors doped with a smaller amount of holes. This suggests that the opening of a large pseudogap is a characteristic property of hole-doped iron-based superconductors.