A temperature dependent tunneling study of the spin density wave gap in EuFe₂As₂single crystals

Abstract

We report temperature dependent scanning tunneling microscopy and spectroscopy measurements on single crystals of EuFe2As2 in the 15-292 K temperature range. The in situ cleaved crystals show atomic terraces with homogeneous tunnel spectra that correlate well with the spin density wave (SDW) transition at a temperature, TSDW ≈ 186 K. Above TSDW the local tunnel spectra show a small depression in the density of states (DOS) near the Fermi energy (EF). The gap becomes more pronounced upon entering the SDW state with a gap value ∼90 meV at 15 K. However, the zero bias conductance remains finite down to 15 K indicating a finite DOS at the EF in the SDW phase. Furthermore, no noticeable change is observed in the DOS at the antiferromagnetic ordering transition of Eu(2+) moments at 19 K.

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

“…Another optical investigation () on EuFeAs also does not show the second gap. Our earlier tunneling study () on EuFeAs also showed a single gap like spectra.…”

“…Some ARPES studies show an energy gap , while others do not show any gap in the SDW state. However, optical conductivity , quantum oscillation and scanning tunneling microscopy and spectroscopy (STM/S) () studies show an energy gap below the SDW transition. In pnictides, both SDW and SC originate from the same Fe d‐bands.…”

Magneto-orbital coupling in iron pnictides

“…Also, as inferred from the results of infrared studies, short-range AF correlations have been suggested as being responsible for the pseudogap in iron superconductors [29,30]. Moreover, scanning tunneling microscopy (STM) studies have also seen an energy gap in the density of states near the Fermi energy [31,32].…”

Electronic inhomogeneities in the superconducting phase of CaFe 1.96 Ni 0.04 As 2 single crystals

“…With its atomic scale structural and spectroscopic imaging capabilities, scanning tunneling microscopy and spectroscopy (STM/S) is an ideal probe to investigate the local electronic properties of these systems. In our variable temperature STM/S we investigate the tem- while we normalize the spectra for large bias (250 mV) to normalize away the effect of the tunnel matrix element on the spectra 22 . This process also sharpens the spectral features.…”