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Single-Crystal Growth and Small Anisotropy of the Lower Critical Field in Oxypnictides: NdFeAsO1 − xFx

1
Institute of Physics, Goethe University Frankfurt, 60438 Frankfurt/M, Germany
2
Lyman Laboratory of Physics, Harvard University, Cambridge, MA 02138, USA
3
Department of Physics and Astronomy, Box 516, Uppsala University, SE-75120 Uppsala, Sweden
*
Author to whom correspondence should be addressed.
Crystals 2020, 10(5), 362; https://doi.org/10.3390/cryst10050362
Received: 7 April 2020 / Revised: 21 April 2020 / Accepted: 22 April 2020 / Published: 1 May 2020
(This article belongs to the Special Issue Growth, Characterization and Modeling of Emergent Materials)
High-quality single crystals of the unconventional superconductor NdFeAsO1 − xFx were grown. We developed a new optimized flux technique to overcome the difficulties in single-crystal growth and the sample quality limitations of NdFeAsO1 − xFx. The normal state of the F-doped samples exhibits simple metallic behavior upon cooling down from room temperature, followed by a sharp superconducting transition. The values of residual resistivity ratio (RRR) is 3.2, 6.4, and 10.3 for x = 0.1, 0.15, and 0.2, respectively. Both the large RRR and the narrow superconducting transition signpost the high quality of the crystals. We have examined the in- and out-of-plane lower critical fields, and the field at which vortices penetrate the sample of NdFeAsO1 − xFx (x = 0.1). The anisotropy ratio [γHc1 (0)] increased slightly with increasing temperature from 0.8 Tc to Tc. The temperature dependence of the first vortex penetration field was obtained under the static magnetic field, H, parallel to the c- and ab- axis, and pronounced changes in the Hc1(T) curvature were observed, which are attributed to the multi-band superconductivity. View Full-Text
Keywords: crystal growth; unconventional superconductor; lower critical field crystal growth; unconventional superconductor; lower critical field
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Hanna, A.R.N.; Abdel-Hafiez, M. Single-Crystal Growth and Small Anisotropy of the Lower Critical Field in Oxypnictides: NdFeAsO1 − xFx. Crystals 2020, 10, 362.

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