Effect of Vacuum Annealing on Superconductivity in Fe(Se,Te) Single Crystals

Abstract

The effect of vacuum annealing on superconductivity is investigated in Fe(Se,Te) single crystals. It is found that superconductivity is not enhanced by annealing under high vacuum ($10 À3 Pa) or by annealing in a sealed evacuated quartz tube. In a moderate vacuum atmosphere ($1 Pa), iron oxide layers are found to show up on sample surfaces, which would draw excess Fe out of the crystal. Thus, it is suggested that remanent oxygen effectively works to remove excess Fe from the matrix of Fe(Se,Te) crystals, resulting improvement of superconducting transition temperature. Our transport measurements suggest that the excess Fe scatters the carriers on electron-and hole-type channels in a different manner. We discuss how the mobility of two types of carriers correlate with superconductivity. Since both the electron and hole bands are important for the occurrence of superconductivity, excess Fe would suppress superconductivity mainly due to strong scattering of electrons.

Exceptional suppression of flux-flow resistivity in FeSe0.4Te0.6 by back-flow from excess Fe atoms and Okada1, Nabeshima2, Takahashi3 et al. 2015Phys. Rev. BSelf Cite232220View full textAdd to dashboardCite

“…Therefore, α < 1 is a manifestation of the intrinsic back-flow phenomenon remarkable in highly-disordered SCs. Returning to the case of FeSe 1−x Te x , excess-Fe atoms are well-known to act as magnetic impurities [23,24]. Thus, it is expected that FeSe 1−x Te x with excess-Fe atoms behaves similarly to conventional SCs with paramagnetic impurities, and we consider that the observed small α of FeSe 0.4 Te 0.6 also originates from the intrinsic back-flow phenomenon.…”

“…To elucidate the role of impurity scattering for ρ f (B), we focused on the FeSe 1−x Te x system. It is well known that excess-Fe atoms enter Fe-(II) sites easily and act as magnetic impurities [23,24]. Therefore, FeSe 1−x Te x is an appropriate materials for investigating ρ f (B) of Fe-SCs with strong impurity scattering.…”

Review of annealing effects and superconductivity in Fe1+y Te1−x Se x superconductors

“…Fig. 13 Oxygen was not detected in the inner part of the annealed crystals after peeling off the surfaces, which proves that the oxygen is not doped into the crystal [42].…”

“…On the as annealed surface, almost no Se or Te is detected. Reprinted with permission from[42]. Copyright 2013 by the Physical Society of Japan.…”

Point-contact Andreev-reflection spectroscopy in Fe(Te,Se) films: multiband superconductivity and electron-boson coupling

“…[21], by the Bridgman method starting from stoichiometrically weighed Fe (99.99% pure), Se (99.999% pure) and Te (99.999% pure). The as-grown crystals were then annealed in a moderate vacuum atmosphere (≃ 1 Pa).…”