Discovery of a pair density wave state in a monolayer high-Tc iron-based superconductor

TL;DR

This paper reports the first experimental observation of a pair density wave state in a monolayer iron-based high-Tc superconductor using scanning tunneling microscopy, revealing a new state that coexists with charge order.

Contribution

It provides the first direct evidence of a PDW state in an iron-based superconductor, expanding understanding of unconventional pairing mechanisms.

Findings

PDW state observed at domain walls with a period of ~3.6a_Fe

PDW coexists with charge density wave order

PDW characterized by local density of states and phase shifts

Abstract

The pair density wave (PDW) is an extraordinary superconducting state where Cooper pairs carry nonzero momentum. It can emerge when the full condensation of zero momentum Cooper pairs is frustrated. Evidence for the existence of intrinsic PDW order in high-temperature (high-Tc) cuprate superconductors and kagome superconductors has emerged recently. However, the PDW order in iron-based high-Tc superconductors has not been observed experimentally. Here, using scanning tunneling microscopy/spectroscopy, we report the discovery of the PDW state in monolayer iron-based high-Tc Fe(Te,Se) films grown on SrTiO3(001) substrates. The PDW state with a period of {\lambda}~3.6a_Fe (a_Fe is the distance between neighboring Fe atoms) is observed at the domain walls by the spatial electronic modulations of the local density of states, superconducting gap, and the {\pi}-phase shift boundaries of the PDW around the dislocations of the intertwined charge density wave order. The discovery of the PDW state in the monolayer Fe(Te,Se) film provides a low-dimensional platform to study the interplay between the correlated electronic states and unconventional Cooper pairing in high-Tc superconductors.