Tunneling spectroscopy and transport properties of FeSe thin films
Final Report Abstract
The presumably unconventional superconductor β-FeSe was deposited by radio frequency sputtering and molecular beam epitaxy (MBE) from two elementary sources. Superconducting thin films were grown in (001)-orientation on MgO(100) and YAlO3(010) substrates. The morphology of the samples was studied and directly related to the superconducting properties of the β-FeSe thin films. The MBE grown thin films show microcracks down to the substrate and a roughness of ≃ 100 nm. In contrast, sputter deposited superconducting thin films show a smooth surface with almost no precipitates. In both cases resistive superconducting transitions with critical temperature up to T midpoint c ≃ 8.5 K were observed. However, the smoothness of the sputter deposited films is crucial for future surface dependent investigations. The superconducting state of FeSe was investigated by tunneling spectroscopy on planar FeSe/AlOx/Ag junctions. By an evaluation of the bias voltage dependent differential conductivities of junctions in the tunneling, intermediate barrier strength, and metallic regimes common features could be identified and associated with the superconducting density of states. Specifically, four characteristic features were observed. Whereas two of them show clear properties of superconducting gaps with 2∆B/kBTc = 5.4 − 6.8 and 2∆D/kBTc = 15.3 − 24.3, the interpretation is less clear for the other two. There are indications of a strong coupling effect with a boson excitation with ωboson ≈ 1.8meV as previously proposed by Song et al. The fourth feature with 2ΓA/kBTc = 1.3 − 3.8 is presumably an impurity induced resonance state in the superconducting energy gap.
Publications
- Thin Film Growth of Fe-based Superconductors: From Fundamental Properties to Functional Devices. A comparative review. Rep. Prog. Phys. 77, 046502 (2014)
S. Haindl, M. Kidszun, S. Oswald, C. Hess, B. Büchner, S. Kölling, L. Wilde, T. Thersleff, M. Jourdan, H. Hiramatsu, H. Hosono
(See online at https://doi.org/10.1088/0034-4885/77/4/046502) - Morphology of superconducting FeSe thin films deposited by co-sputtering and MBE
Eike Venzmer, Alexander Kronenberg, Janek Maletz, and Martin Jourdan
- Multiple energy gap features of superconducting FeSe investigated by tunneling spectroscopy
Eike Venzmer, Alexander Kronenberg, and Martin Jourdan
