Weakening of the spin density wave gap at low temperatures in SrFe$_2$As$_2$ single crystals

TL;DR

This study uses scanning tunneling microscopy and spectroscopy to investigate how the spin density wave gap in SrFe$_2$As$_2$ changes with temperature, revealing a weakening of the gap at low temperatures that may facilitate superconductivity.

Contribution

It provides detailed temperature-dependent tunneling data showing the SDW gap weakening, suggesting a precursor role for superconductivity in SrFe$_2$As$_2$.

Findings

SDW transition at approximately 205 K

Partial energy gap decreases as temperature lowers

Potential nucleation sites for superconductivity near defects

Abstract

We report on temperature dependent scanning tunneling microscopy and spectroscopy studies of undoped SrFe$_{2}$As$_{2}$ single crystals from 6 K to 292 K. Resistivity data show spin density wave (SDW) transition at T$_{SDW}$ $\approx$ 205 K and the superconducting transition at $\sim$ 21 K while magnetic susceptibility does not show any superconductivity. Conductance maps and local tunneling spectra show an electronically homogeneous surface at all studied temperatures. Tunnel spectra correlate well with the SDW transition with a depression in the density of states near the Fermi energy below T$_{SDW}$. 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.