The number and the symmetry of the order parameter(s) (OPs) in Fe-based superconductors, as well as the occurrence of anisotropic or nodal OP symmetries are important topics at the center of the present scientific debate. We show here that when accurate point-contact Andreev-reflection (PCAR) experiments in good-quality samples are carried out by different groups they do provide surprisingly consistent results. Moreover, the analysis of directional PCAR results in complex materials requires enhanced theoretical tools. We recently extended the theoretical model for Andreev reflection to the full 3D case accounting for Fermi surfaces of (almost) arbitrary shape. This combined theoretical/experimental approach allows us to conclude that, in the most studied La 1111, Sm 1111, Co-doped and K-doped Ba 122 compounds around optimal doping, the available high-quality PCAR results agree rather well on the presence of two isotropic gaps. On the other hand, our recent directional PCAR results on single crystals of the Ca 122 family clearly show the presence of at least one nodal (or strongly anisotropic) OP, possibly in agreement with recent theoretical predictions.

Directional point-contact Andreev-reflection spectroscopy of Fe-based superconductors: Gap symmetry and Fermi surface topology / Gonnelli, Renato; Tortello, Mauro; Daghero, Dario; Ummarino, Giovanni; V. A., Stepanov; Z., Bukowski; N. D., Zhigadlo; J., Karpinski; J., Jiang; P., Reuvekamp; R. K., Kremer. - STAMPA. - (2011). (Intervento presentato al convegno Superconductivity 100 years later: A computational Approach tenutosi a Porto Conte, Alghero, Italy nel 15-18th September 2011).

Directional point-contact Andreev-reflection spectroscopy of Fe-based superconductors: Gap symmetry and Fermi surface topology

GONNELLI, Renato;TORTELLO, MAURO;DAGHERO, Dario;UMMARINO, Giovanni;
2011

Abstract

The number and the symmetry of the order parameter(s) (OPs) in Fe-based superconductors, as well as the occurrence of anisotropic or nodal OP symmetries are important topics at the center of the present scientific debate. We show here that when accurate point-contact Andreev-reflection (PCAR) experiments in good-quality samples are carried out by different groups they do provide surprisingly consistent results. Moreover, the analysis of directional PCAR results in complex materials requires enhanced theoretical tools. We recently extended the theoretical model for Andreev reflection to the full 3D case accounting for Fermi surfaces of (almost) arbitrary shape. This combined theoretical/experimental approach allows us to conclude that, in the most studied La 1111, Sm 1111, Co-doped and K-doped Ba 122 compounds around optimal doping, the available high-quality PCAR results agree rather well on the presence of two isotropic gaps. On the other hand, our recent directional PCAR results on single crystals of the Ca 122 family clearly show the presence of at least one nodal (or strongly anisotropic) OP, possibly in agreement with recent theoretical predictions.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11583/2503849
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