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

摘要

We report a scanning tunneling spectroscopy investigation of polycrystallineSmFeAsO0.85 having a superconducting transition at 52 K. On large regions ofthe sample surface the tunneling spectra exhibited V-shaped gap structures withno coherence peaks, indicating degraded surface properties. In some regions,however, the coherence peaks were clearly observed, and the V-shaped gaps couldbe fit to the theory of tunneling into a d-wave superconductor, yielding gapvalues 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 thespectra exhibited zero-bias conductance peaks, consistent with a d-wave orderparameter symmetry.