Scanning tunneling spectroscopy of SmFeAsO0.85: Possible evidence for d-wave order parameter symmetry

TL;DR

This study uses scanning tunneling spectroscopy on SmFeAsO0.85 to find evidence suggesting a d-wave symmetry of the superconducting order parameter, based on gap structures and zero-bias conductance peaks.

Contribution

It provides experimental evidence for d-wave order parameter symmetry in SmFeAsO0.85, a Fe-based superconductor, through detailed surface spectroscopy analysis.

Findings

V-shaped gap structures with no coherence peaks on large surface regions

Observation of coherence peaks in some regions fitting d-wave superconductor theory

Detection of zero-bias conductance peaks consistent with d-wave symmetry

Abstract

We report a scanning tunneling spectroscopy investigation of polycrystalline SmFeAsO0.85 having a superconducting transition at 52 K. On large regions of the sample surface the tunneling spectra exhibited V-shaped gap structures with no coherence peaks, indicating degraded surface properties. In some regions, however, the coherence peaks were clearly observed, and the V-shaped gaps could be fit to the theory of tunneling into a d-wave superconductor, yielding gap values between 8 to 8.5 meV, corresponding to the ratio 2D/KTc ~ 3.55 - 3.8, which is slightly above the BCS weak-coupling prediction. In other regions the spectra exhibited zero-bias conductance peaks, consistent with a d-wave order parameter symmetry.