Unconventional London penetration depth in Ba(Fe0.93Co0.07)2As2 single crystals

Abstract

The London penetration depth, $\lambda (T)$, has been measured in several single crystals of Ba(Fe${}_{0.93}$Co${}_{0.07}$)${}_2$As${}_2$. Thermodynamic, electromagnetic, and structural characterization measurements confirm that these crystals are of excellent quality. The observed low temperature variation of $\lambda (T)$ follows a power-law, $\Delta \lambda (T)\sim T^n$ with $n=2.4\pm 0.1$, indicating the existence of normal quasiparticles down to at least $0.02T_c$. This is in contrast to recent penetration depth measurements on single crystals of NdFeAsO${}_{1-x}$F${}_x$ and SmFeAsO${}_{1-x}$F${}_x$, which indicate an anisotropic but nodeless gap. We propose that a more three-dimensional character in the electronic structure of Ba(Fe${}_{0.93}$Co${}_{0.07}$)${}_2$As${}_2$ may lead to an anisotropic $s-$wave gap with point nodes that would explain the observed $\lambda (T)$.

4 pages

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• Optical properties of the iron-arsenic superconductor BaFe1.85Co0.15As2
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• Superconducting Properties of the $s^{\pm }$-wave state: Fe-based superconductors
• A doping dependent specific heat study of the superconducting gap in Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$
• DC superconducting quantum interference devices fabricated using bicrystal grain boundary junctions in Co-doped BaFe2As2 epitaxial films
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• Superfluid Density and Field-Induced Magnetism in Ba(Fe1-xCox)2As2 and Sr(Fe1-xCox)2As2 Measured with Muon Spin Relaxation
• Superconductivity without Fe or Ni in the phosphides BaIr2P2 and BaRh2P2
• Comprehensive Eliashberg analysis of microwave conductivity and penetration depth of K-, Co-, and P-substituted BaFe2As2
• Lower critical field and SNS-Andreev spectroscopy of 122-arsenides: Evidence of nodeless superconducting gap
• Lower Critical Field, Anisotropy, and Two-Gap Features of LiFeAs
• Nodeless superconductivity in the presence of spin-density wave in pnictide superconductors: The case of BaFe${}_{2-x}$Ni${}_x$As${}_2$
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• Calorimetric Evidence for Nodes in the Overdoped Ba(Fe${}_{0.9}$Co${}_{0.1}$)${}_2$As${}_2$
• ${}^{75}$As NMR of Ba(Fe${}_{0.93}$Co${}_{0.07}$)${}_2$As${}_2$ in High Magnetic Field
• The effect of disorder on electronic Raman scattering in the superconducting state of iron pnictides
• Direct measurement of the temperature dependence of the magnetic penetration depth in Ba(Fe${}_{1-x}$Ni${}_x$)${}_2$As${}_2$ superconductors
• Probing Local Variations of Superconductivity on the Surface of Ba(Fe1-xCox)2As2 Single Crystals
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