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Evidence from anisotropic penetration depth for a three-dimensional nodal superconducting gap in single-crystalline Ba(Fe1xNix)2As2

C. Martin, H. Kim, R. T. Gordon, N. Ni, V. G. Kogan, S. L. Bud’ko, P. C. Canfield, M. A. Tanatar, and R. Prozorov
Phys. Rev. B 81, 060505(R) – Published 17 February 2010

Abstract

The London penetration depth, λ, is directly related to the density, ns, of the Cooper pairs (λ21/ns) and its variation with temperature provides valuable insight into the pairing mechanism. Here we study the evolution with doping of the temperature dependence of the in-plane (λab) and out-of-plane (λc) penetration depths in single crystals of electron-doped Ba(Fe1xNix)2As2. As is the case for other pnictides, λ(T)Tn over the whole doping range and this behavior extends down to at least T=Tc/100, setting a very small upper limit on the gap minimum. Furthermore, in the overdoped regime: (1) the exponent n becomes substantially smaller than 2, which is incompatible with the models that explain power-law behavior to be due to scattering; (2) the exponent n becomes anisotropic, with λc(T) showing a clear T-linear behavior over a large temperature interval. These findings suggest that in the overdoped regime the superconducting gap in iron-based pnictide superconductors develops nodal structure, which unlike in the cuprates, cannot be understood within a two-dimensional picture.

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  • Received 13 January 2010

DOI:https://doi.org/10.1103/PhysRevB.81.060505

©2010 American Physical Society

Authors & Affiliations

C. Martin, H. Kim, R. T. Gordon, N. Ni, V. G. Kogan, S. L. Bud’ko, P. C. Canfield, M. A. Tanatar, and R. Prozorov*

  • Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA

  • *Corresponding author; prozorov@ameslab.gov

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Issue

Vol. 81, Iss. 6 — 1 February 2010

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