Weakening of the spin density wave gap at low temperatures in single crystals

Abstract

We report on temperature dependent scanning tunneling microscopy and spectroscopy studies of undoped SrFe2As2 single crystals from 6 to 292 K. Resistivity data show spin density wave (SDW) transition at TSDW ≈205 K and the superconducting transition at ∼21 K while magnetic susceptibility does not show any superconductivity. Tunnel spectra correlate well with the SDW transition with a depression in the density of states near the Fermi energy below TSDW. On further lowering the temperature, the width of this partial energy gap associated with the SDW decreases. Using the anti‐correlation of superconducting phase with SDW, we interpret this gap weakening as a precursor to superconductivity. This may give rise to a facile nucleation of superconductivity near defects.