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Sci Rep. 2017 Aug 30;7(1):9994. doi: 10.1038/s41598-017-10383-1.

Origin of the emergence of higher T c than bulk in iron chalcogenide thin films.

Author information

1
School of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju, 61005, South Korea.
2
Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, 53706, USA.
3
Department of Physics, Kyungpook National University, Daegu, 41566, South Korea.
4
Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, 32310, USA.
5
Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York, 11973, USA.
6
Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, 100871, China.
7
School of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju, 61005, South Korea. sanghan@gist.ac.kr.

Abstract

Fabrication of epitaxial FeSexTe1-x thin films using pulsed laser deposition (PLD) enables improving their superconducting transition temperature (T c) by more than ~40% than their bulk T c. Intriguingly, T c enhancement in FeSexTe1-x thin films has been observed on various substrates and with different Se content, x. To date, various mechanisms for T c enhancement have been reported, but they remain controversial in universally explaining the T c improvement in the FeSexTe1-x films. In this report, we demonstrate that the controversies over the mechanism of T c enhancement are due to the abnormal changes in the chalcogen ratio (Se:Te) during the film growth and that the previously reported T c enhancement in FeSe0.5Te0.5 thin films is caused by a remarkable increase of Se content. Although our FeSexTe1-x thin films were fabricated via PLD using a Fe0.94Se0.45Te0.55 target, the precisely measured composition indicates a Se-rich FeSexTe1-x (0.6 < x < 0.8) as ascertained through accurate compositional analysis by both wavelength dispersive spectroscopy (WDS) and Rutherford backscattering spectrometry (RBS). We suggest that the origin of the abnormal composition change is the difference in the thermodynamic properties of ternary FeSexTe1-x, based on first principle calculations.

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