Temperature and Spatial Dependence of the Superconducting and Pseudogap of NdFeAsO0.86F0.14

TL;DR

This study uses scanning tunneling microscopy to investigate the temperature-dependent superconducting and pseudogap behaviors in NdFeAsO0.86F0.14, revealing spatially varying gaps and their relation to superconductivity and pseudogap phenomena.

Contribution

First spatially resolved measurements of superconducting and pseudogap features in NdFeAsO0.86F0.14, highlighting the coexistence and competition of gaps in an iron-based superconductor.

Findings

Presence of two distinct gaps below Tc with different spatial distributions

Observation of a pseudogap opening above Tc at specific locations

Superconducting and pseudogap order parameters exhibit competition

Abstract

The discovery of superconductivity with a critical temperature exceeding 55 K in the iron-oxypnictides and related compounds has quite suddenly given the community a new set of materials - breaking the tyranny of copper. This new class of materials raises fundamental questions related to the origin of the electron pairing in the superconducting state and to the similarity to superconductivity in the cuprates. Here, we report spatially resolved measurements using scanning tunneling microscopy/spectroscopy (STM/STS) of the newly discovered iron-based layered superconductor NdFeAsO0.86F0.14 (Tc = 48 K) as a function of temperature. The tunneling spectra at 17 K show a suppression of spectral intensity within +/- 10 meV, indicative of the opening of the superconducting gap (SG). Below Tc, the sample exhibits two characteristic gaps - a large one (18 meV) and a small one (9 meV) - existing in different spatial locations. Both gaps are closed above Tc at the bulk Tc, but only the small gap can be fitted with a superconducting gap function. This gap displays a BCS - like order parameter. Above Tc, at the same location where the small gap was observed, a pseudogap (PG) opens abruptly at a temperature just above Tc and closes at 120 K. In contrast to the cuprates, the SG and PG have competing order parameters.