The unique properties of superconducting materials open the way to a wide range of applications e.g. in the fields of electronics, medicine, research and energy. Up to now, metallic superconductors are already widely used in medical diagnostics or as high field research magnets. However, unconventional superconductors as high-Tc cuprates or Fe-based superconductors have the potential to extend this application range significantly due to their unique properties as high critical transition temperatures or magnetic fields. Therefore, the central aim of this research topic is to investigate superconducting materials as well as to develop small devices or demonstrator systems for applications in an industrial environment. Our research covers the preparation of thin films to study key properties of new superconducting materials, the detailed characterization of coated conductors to optimize their functional properties and the application of superconducting magnetic bearings for improved technological processes.
F. Rizzo, A. Augieri, A. Kursumovic, M. Bianchetti, L. Opherden, M. Sieger, R. Hühne, J. Hänisch, A. Meledin, G. Van Tendeloo, J. L. MacManus-Driscoll and G. Celentano,
Nanoscale, 2018, 10, 8187
An outstanding current carrying performance (namely critical current density, Jc) over a broad temperature range of 10–77 K for magnetic fields up to 12 T is reported for films of YBa2Cu3O7−x with Ba2Y(Nb,Ta)O6 inclusion pinning centres (YBCO-BYNTO) and thicknesses in the range of 220–500 nm. Jc values of 10 MA cm−2 were measured at 30 K – 5 T and 10 K – 9 T with a corresponding maximum of the pinning force density at 10 K close to 1 TN m−3. The system is very flexible regarding properties and microstructure tuning, and the growth window for achieving a particular microstructure is wide, which is very important for industrial processing. Hence, the dependence of Jc on the magnetic field angle was readily controlled by fine tuning the pinning microstructure. Transmission electron microscopy (TEM) analysis highlighted that higher growth rates induce more splayed and denser BYNTO nanocolumns with a matching field as high as 5.2 T. Correspondingly, a strong peak at the B||c-axis is noticed when the density of vortices is lower than the nanocolumn density. YBCO-BYNTO is a very robust and reproducible composite system or high-current coated conductors over an extended range of magnetic fields and temperatures.
Y. Naidyuk, O. Kvitnitskaya, D. Bashlakov, S. Aswartham, I. Morozov, I. Chernyavskii, G. Fuchs, S.-L. Drechsler, R. Hühne, K. Nielsch, B. Büchner, D. Efremov,
2D Mater. 5 (2018) 045014
MoTe2 is a Weyl semimetal, which exhibits unique non-saturating magnetoresistance and strongly reinforced superconductivity under pressure. Here, we demonstrate that a novel mesoscopic superconductivity at ambient pressure arises on the surface of MoTe2 with a critical temperature up to 5 K significantly exceeding the bulk Tc = 0.1 K. We measured the derivatives of I–V curves for hetero-contacts of MoTe2 with Ag or Cu, homo-contacts of MoTe2 as well as 'soft' point contacts (PCs). Large number of these hetero-contacts exhibit a dV/dI dependence, which is characteristic for Andreev reflection. It allows us to determine the superconducting gap Δ. The average gap values are 2Δ = 1.30 ± 0.15 meV with a 2Δ/kBTc ratio of 3.7 ± 0.4, which slightly exceeds the standard BCS value of 3.52. Furthermore, the temperature dependence of the gap follows a BCS-like behavior, which points to a nodeless superconducting order parameter with some strong-coupling renormalization. Remarkably, the observation of a 'gapless-like' single minimum in the dV/dI of 'soft' PCs may indicate a topological superconducting state of the MoTe2 surface as these contacts probe mainly the interface and avoid additional pressure effect. Therefore, MoTe2 might be a suitable material to study new forms of topological superconductivity.
A. Pukenas, P. Chekhonin, M. Meißner, E. Hieckmann, S. Aswartham, J. Freudenberger, J. Engelmann, R. Hühne, S. Wurmehl, B. Büchner, W. Skrotzki,
Micron 119 (2019) 1-7
The ternary iron arsenide compound BaFe2As2 exhibits a structural phase transition from tetragonal to orthorhombic at a temperature of about 140 K. The twin lamellae arising below this transition temperature were studied in undoped single crystalline bulk and epitaxial thin film samples using electron backscatter diffraction in a scanning electron microscope equipped with a helium cryostat. Applying this technique on bulk single crystals a characteristic twin lamella size in the range of 0.1 μm up to a few μm was observed. In contrast, in epitaxially strained thin films the phase transition is not observed at temperatures above 19 K.